Add rtc_use_memcheck flag, update MB and GN to handle it, and add gni files listing the runtime deps

webrtc/base/BUILD.gn

Index: webrtc/base/BUILD.gn
diff --git a/webrtc/base/BUILD.gn b/webrtc/base/BUILD.gn
index 1d258058720b1846f71aa2e891e5551cab6f36d4..97343c5a3e6a6444ce633c6ccdb484aa43bb7801 100644
--- a/webrtc/base/BUILD.gn
+++ b/webrtc/base/BUILD.gn
@@ -17,6 +17,9 @@ if (is_android) {
 if (is_win) {
   import("//build/config/clang/clang.gni")
 }
+if (rtc_use_memcheck) {
+  import("memcheck_dependencies.gni")
+}
 
 group("base") {
   public_deps = [
@@ -210,6 +213,10 @@ rtc_static_library("rtc_base_approved") {
       "logging_mac.mm",
     ]
   }
+  data = []

[kjellander_webrtc, 2016/11/21 08:33:59]

I think we should only add memcheck_dependencies for test targets, so this
should probably live in //webrtc/test:test_support instead. That said, you
probably need to make sure all test targets depend on it. I suspect there might
be some that don't.

+  if (rtc_use_memcheck) {
+    data += memcheck_dependencies
+  }
   if (is_component_build && is_win) {
     # Copy the VS runtime DLLs into the isolate so that they don't have to be
     # preinstalled on the target machine. The debug runtimes have a "d" at
@@ -226,7 +233,7 @@ rtc_static_library("rtc_base_approved") {
 
     # These runtime files are copied to the output directory by the
     # vs_toolchain script that runs as part of toolchain configuration.
-    data = [
+    data += [

[kjellander_webrtc, 2016/11/21 08:33:59]

I'm not sure these belong in rtc_base_approved target for Windows. Having them
here means they'll be copied to the output  directory for Windows builds,
doesn't it? I wonder if we should investigate if they're only needed for Windows
unit test executables. It could be worth asking a Windows expert like tommi@
about this (file a separate bug)

[ehmaldonado_webrtc, 2016/11/22 15:16:01]

Yes, this is only needed for executing Windows tests on swarming. We might move
them also to test_support, but that's for another CL.
I filed https://bugs.chromium.org/p/webrtc/issues/detail?id=6746 for that.

       "$root_out_dir/msvcp140${vcrt_suffix}.dll",
       "$root_out_dir/vccorlib140${vcrt_suffix}.dll",
       "$root_out_dir/vcruntime140${vcrt_suffix}.dll",