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This CL adds a histogram to measure how often a CSS transition is
cancelled by removing the transition style.

Bug: 934700
Change-Id: I53f608f0e4cf2ec07adaecb879cffbb557ce2753
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1632714Reviewed-by: Xida Chen <xidachen@chromium.org>
Reviewed-by: Stephen McGruer <smcgruer@chromium.org>
Commit-Queue: Xida Chen <xidachen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#664323}