The name of the histogram is V8.GCIncrementalMarkingSum.

Bug: chromium:756592
Change-Id: Ib073e846054550cce8558a3a577a0451e3182407
Reviewed-on: https://chromium-review.googlesource.com/618877
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47422}