Reland of Make it possible for tests to set up trace event handlers.

Reland of Make it possible for tests to set up trace event handlers. (patchset #1 id:1 of https://codereview.webrtc.org/2997963002/ )

Reason for revert:
This should fix it

Original issue's description:
> Revert of Make it possible for tests to set up trace event handlers. (patchset #4 id:60001 of https://codereview.webrtc.org/3002663002/ )
> 
> Reason for revert:
> Breaks Chromium bots.
> https://build.chromium.org/p/chromium.webrtc.fyi/builders/Mac%20Builder/builds/27340/steps/generate_build_files/logs/stdio
> 
> Original issue's description:
> > Make it possible for tests to set up trace event handlers.
> > 
> > As it is now, the first time a TRACE_EVENT... is called, the result from
> > the current handler is stored in a static const variable, and subsequent
> > calls will use that value regardless of changes to the handler.
> > 
> > This is a problem if a test wants to use another handler.
> > 
> > BUG=None
> > 
> > Review-Url: https://codereview.webrtc.org/3002663002
> > Cr-Commit-Position: refs/heads/master@{#19382}
> > Committed: https://chromium.googlesource.com/external/webrtc/+/a9732656221e0033ab93ecf01cf07f71817da1e8
> 
> TBR=hbos@webrtc.org,kwiberg@webrtc.org,mbonadei@webrtc.org,kjellander@webrtc.org
> # Skipping CQ checks because original CL landed less than 1 days ago.
> NOPRESUBMIT=true
> NOTREECHECKS=true
> NOTRY=true
> BUG=None
> 
> Review-Url: https://codereview.webrtc.org/2997963002
> Cr-Commit-Position: refs/heads/master@{#19383}
> Committed: https://chromium.googlesource.com/external/webrtc/+/db758c2589a983a7dd94dfdd9272892e28251fe4

TBR=hbos@webrtc.org,kwiberg@webrtc.org,mbonadei@webrtc.org,kjellander@webrtc.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=None

Review-Url: https://codereview.webrtc.org/2995123002
Cr-Commit-Position: refs/heads/master@{#19386}
Committed: https://chromium.googlesource.com/external/webrtc/+/481c549b29bab2e5314204884a117c9669846111

[ehmaldonado_webrtc, 2017-08-17 13:56:11]

Created Reland of Make it possible for tests to set up trace event handlers.

[mbonadei, 2017-08-17 14:02:50]

https://codereview.webrtc.org/2995123002/diff/70001/webrtc/BUILD.gn
File webrtc/BUILD.gn (right):

https://codereview.webrtc.org/2995123002/diff/70001/webrtc/BUILD.gn#newcode41
webrtc/BUILD.gn:41: defines += [
Oh... This was a well hidden bug. :)

I thought that GN should complain if you try to override an already defined
variable.

[mbonadei, 2017-08-17 14:03:13]

lgtm is the bot is green.

[ehmaldonado_webrtc, 2017-08-17 14:05:13]

https://codereview.webrtc.org/2995123002/diff/70001/webrtc/BUILD.gn
File webrtc/BUILD.gn (right):

https://codereview.webrtc.org/2995123002/diff/70001/webrtc/BUILD.gn#newcode41
webrtc/BUILD.gn:41: defines += [
On 2017/08/17 14:02:50, mbonadei wrote:
> Oh... This was a well hidden bug. :)
> 
> I thought that GN should complain if you try to override an already defined
> variable.

It did, hence the failure to generate build files in the Chromium bot. The
WebRTC bots didn't catch this because build_with_chromium is false.

[mbonadei, 2017-08-17 14:08:34]

https://codereview.webrtc.org/2995123002/diff/70001/webrtc/BUILD.gn
File webrtc/BUILD.gn (right):

https://codereview.webrtc.org/2995123002/diff/70001/webrtc/BUILD.gn#newcode41
webrtc/BUILD.gn:41: defines += [
On 2017/08/17 14:05:13, ehmaldonado_webrtc wrote:
> On 2017/08/17 14:02:50, mbonadei wrote:
> > Oh... This was a well hidden bug. :)
> > 
> > I thought that GN should complain if you try to override an already defined
> > variable.
> 
> It did, hence the failure to generate build files in the Chromium bot. The
> WebRTC bots didn't catch this because build_with_chromium is false.

I see... Yeah, I didn't look at the failure. :)

[kwiberg-webrtc, 2017-08-17 14:11:33]

lgtm

[ehmaldonado_webrtc, 2017-08-17 14:59:41]

The CQ bit was checked by ehmaldonado@webrtc.org

[commit-bot: I haz the power, 2017-08-17 14:59:48]

CQ is trying da patch.

Follow status at:
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.webrtc.org/...

[commit-bot: I haz the power, 2017-08-17 14:59:55]

CQ is committing da patch.

Bot data: {"patchset_id": 70001, "attempt_start_ts": 1502981981899420,
"parent_rev": "6b463faccbf145b54b8fb2666bfeab868256df08", "commit_rev":
"481c549b29bab2e5314204884a117c9669846111"}

[commit-bot: I haz the power, 2017-08-17 14:59:59]

Description was changed from

==========
Reland of Make it possible for tests to set up trace event handlers. (patchset
#1 id:1 of https://codereview.webrtc.org/2997963002/ )

Reason for revert:
This should fix it

Original issue's description:
> Revert of Make it possible for tests to set up trace event handlers. (patchset
#4 id:60001 of https://codereview.webrtc.org/3002663002/ )
> 
> Reason for revert:
> Breaks Chromium bots.
>
https://build.chromium.org/p/chromium.webrtc.fyi/builders/Mac%20Builder/build...
> 
> Original issue's description:
> > Make it possible for tests to set up trace event handlers.
> > 
> > As it is now, the first time a TRACE_EVENT... is called, the result from
> > the current handler is stored in a static const variable, and subsequent
> > calls will use that value regardless of changes to the handler.
> > 
> > This is a problem if a test wants to use another handler.
> > 
> > BUG=None
> > 
> > Review-Url: https://codereview.webrtc.org/3002663002
> > Cr-Commit-Position: refs/heads/master@{#19382}
> > Committed:
https://chromium.googlesource.com/external/webrtc/+/a9732656221e0033ab93ecf01...
> 
>
TBR=hbos@webrtc.org,kwiberg@webrtc.org,mbonadei@webrtc.org,kjellander@webrtc.org
> # Skipping CQ checks because original CL landed less than 1 days ago.
> NOPRESUBMIT=true
> NOTREECHECKS=true
> NOTRY=true
> BUG=None
> 
> Review-Url: https://codereview.webrtc.org/2997963002
> Cr-Commit-Position: refs/heads/master@{#19383}
> Committed:
https://chromium.googlesource.com/external/webrtc/+/db758c2589a983a7dd94dfdd9...

TBR=hbos@webrtc.org,kwiberg@webrtc.org,mbonadei@webrtc.org,kjellander@webrtc.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=None
==========

to

==========
Reland of Make it possible for tests to set up trace event handlers. (patchset
#1 id:1 of https://codereview.webrtc.org/2997963002/ )

Reason for revert:
This should fix it

Original issue's description:
> Revert of Make it possible for tests to set up trace event handlers. (patchset
#4 id:60001 of https://codereview.webrtc.org/3002663002/ )
> 
> Reason for revert:
> Breaks Chromium bots.
>
https://build.chromium.org/p/chromium.webrtc.fyi/builders/Mac%20Builder/build...
> 
> Original issue's description:
> > Make it possible for tests to set up trace event handlers.
> > 
> > As it is now, the first time a TRACE_EVENT... is called, the result from
> > the current handler is stored in a static const variable, and subsequent
> > calls will use that value regardless of changes to the handler.
> > 
> > This is a problem if a test wants to use another handler.
> > 
> > BUG=None
> > 
> > Review-Url: https://codereview.webrtc.org/3002663002
> > Cr-Commit-Position: refs/heads/master@{#19382}
> > Committed:
https://chromium.googlesource.com/external/webrtc/+/a9732656221e0033ab93ecf01...
> 
>
TBR=hbos@webrtc.org,kwiberg@webrtc.org,mbonadei@webrtc.org,kjellander@webrtc.org
> # Skipping CQ checks because original CL landed less than 1 days ago.
> NOPRESUBMIT=true
> NOTREECHECKS=true
> NOTRY=true
> BUG=None
> 
> Review-Url: https://codereview.webrtc.org/2997963002
> Cr-Commit-Position: refs/heads/master@{#19383}
> Committed:
https://chromium.googlesource.com/external/webrtc/+/db758c2589a983a7dd94dfdd9...

TBR=hbos@webrtc.org,kwiberg@webrtc.org,mbonadei@webrtc.org,kjellander@webrtc.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=None

Review-Url: https://codereview.webrtc.org/2995123002
Cr-Commit-Position: refs/heads/master@{#19386}
Committed:
https://chromium.googlesource.com/external/webrtc/+/481c549b29bab2e5314204884...
==========

[commit-bot: I haz the power, 2017-08-17 15:00:00]

Committed patchset #2 (id:70001) as
https://chromium.googlesource.com/external/webrtc/+/481c549b29bab2e5314204884...