Change declarations from var to let/const in runtime_stats_metric.html.

Change declarations from var to let/const in runtime_stats_metric.html.


BUG=chromium:686250

[mythria, 2017-02-21 12:39:26]

The CQ bit was checked by mythria@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2017-02-21 12:39:30]

Dry run: CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2017-02-21 12:53:39]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2017-02-21 12:53:40]

Dry run: Try jobs failed on following builders:
  Catapult Linux Tryserver on master.tryserver.client.catapult (JOB_FAILED,
https://build.chromium.org/p/tryserver.client.catapult/builders/Catapult%20Li...)

[mythria, 2017-03-08 16:02:01]

The CQ bit was checked by mythria@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2017-03-08 16:02:06]

Dry run: CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2017-03-08 16:24:10]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2017-03-08 16:24:12]

Dry run: This issue passed the CQ dry run.

[mythria, 2017-03-08 16:36:53]

mythria@chromium.org changed reviewers:
+ benjhayden@chromium.org

[mythria, 2017-03-08 16:36:54]

Hi Ben, 

I updated runtime_stats_metric.html to use let/const declarations instead of
var. PTAL.

Thanks,
Mythri

[benjhayden, 2017-03-08 18:04:18]

Thanks for doing this!
Sorry the recommendations changed out from under you. :-/
It looks like there's some confusion about when you can use const. It's ok, I'm
still learning this myself. :-)
JS const !== C++ const: JS const variables can be modified, but the name-object
binding cannot be re-assigned.
I think that almost all of these lets can be changed to const.
for..of loops can all use const unless the loop body re-assigns the loop
variable.
C-style for-loops cannot use const because the *crement re-assigns the loop
variable.