CL that changes GC reason strings to enums: https://codereview.chromium.org/2310143002/

The following revision refers to this bug:
  https://chromium.googlesource.com/v8/v8.git/+/371c7a388fed901c7403aa5afbcbff9ee81ce077

commit 371c7a388fed901c7403aa5afbcbff9ee81ce077
Author: ulan <ulan@chromium.org>
Date: Wed Sep 07 13:30:30 2016

[heap] Add histogram counters to track GC reasons.

BUG= chromium:644713 
LOG=NO

Review-Url: https://codereview.chromium.org/2322453002
Cr-Commit-Position: refs/heads/master@{#39250}

[modify] https://crrev.com/371c7a388fed901c7403aa5afbcbff9ee81ce077/src/counters.h
[modify] https://crrev.com/371c7a388fed901c7403aa5afbcbff9ee81ce077/src/heap/gc-tracer.cc
[modify] https://crrev.com/371c7a388fed901c7403aa5afbcbff9ee81ce077/src/heap/heap.h
[modify] https://crrev.com/371c7a388fed901c7403aa5afbcbff9ee81ce077/src/heap/incremental-marking.cc

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/d834cbb00a2f75483219a8f8bb3a40cf05a52134

commit d834cbb00a2f75483219a8f8bb3a40cf05a52134
Author: ulan <ulan@chromium.org>
Date: Thu Sep 08 13:22:25 2016

Register V8 garbage collection reason histograms in histograms.xml

BUG= 644713 

Review-Url: https://codereview.chromium.org/2318103002
Cr-Commit-Position: refs/heads/master@{#417270}

[modify] https://crrev.com/d834cbb00a2f75483219a8f8bb3a40cf05a52134/tools/metrics/histograms/histograms.xml

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/d834cbb00a2f75483219a8f8bb3a40cf05a52134

commit d834cbb00a2f75483219a8f8bb3a40cf05a52134
Author: ulan <ulan@chromium.org>
Date: Thu Sep 08 13:22:25 2016

Register V8 garbage collection reason histograms in histograms.xml

BUG= 644713 

Review-Url: https://codereview.chromium.org/2318103002
Cr-Commit-Position: refs/heads/master@{#417270}

[modify] https://crrev.com/d834cbb00a2f75483219a8f8bb3a40cf05a52134/tools/metrics/histograms/histograms.xml