All graphs for this bug:
  https://chromeperf.appspot.com/group_report?bug_id=786583

(For debugging:) Original alerts at time of bug-filing:
  https://chromeperf.appspot.com/group_report?sid=f7b8ecb80a50df00e921fa71aa1d51327963d01aa8e84b6ce063cc9632954457


Bot(s) for this bug's original alert(s):

chromium-rel-mac11
linux-release

📍 Pinpoint job started.
https://pinpoint-dot-chromeperf.appspot.com/job/16977ea5f80000

📍 Found a significant difference after 1 commit.
https://pinpoint-dot-chromeperf.appspot.com/job/16977ea5f80000

Move OpenTypeVerticalData off of SimpleFontData
By drott@chromium.org · Wed Nov 15 14:22:40 2017
chromium @ 45424ca29a623cba7f167cc1ca1651adcd291540

Understanding performance regressions:
  http://g.co/ChromePerformanceRegressions

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/c0ce7ee036e8b06de2d64bf1e91c00dedf63e447

commit c0ce7ee036e8b06de2d64bf1e91c00dedf63e447
Author: Dominik Röttsches <drott@chromium.org>
Date: Tue Nov 21 04:47:33 2017

Avoid recomputing fallback values for vertical metrics

In https://chromium-review.googlesource.com/#/c/768822/
OpenTypeVerticalData was moved off of SimpleFontData. In order to
compute OpenTypeVerticalData lazily when needed for vertical layout,
fallback metrics ascent, height and size_per_unit need to be
available. This CL triggered two reports of performance regressions
(bugs below). I suspect these stem from a higher overhead in computing
these fallback metrics for every shaping operation. This CL reduces
computing the fallback metrics to situations in which they are needed
because the run's direction is vertical.

Somewhat speculative fix for the bugs below as it is hard to meaure
locally without noise. However, the amount of fallback metrics
recomputation for non-vertical layout pages was reduced from tens of
thousands to zero.

Bug:  786596 ,  786583 
Change-Id: I5b667b3aab4b6346d519768e62f17187905bf090
Reviewed-on: https://chromium-review.googlesource.com/779426
Commit-Queue: Koji Ishii <kojii@chromium.org>
Reviewed-by: Koji Ishii <kojii@chromium.org>
Cr-Commit-Position: refs/heads/master@{#518119}
[modify] https://crrev.com/c0ce7ee036e8b06de2d64bf1e91c00dedf63e447/third_party/WebKit/Source/platform/fonts/FontPlatformData.cpp
[modify] https://crrev.com/c0ce7ee036e8b06de2d64bf1e91c00dedf63e447/third_party/WebKit/Source/platform/fonts/opentype/OpenTypeCapsSupportMPL.cpp
[modify] https://crrev.com/c0ce7ee036e8b06de2d64bf1e91c00dedf63e447/third_party/WebKit/Source/platform/fonts/shaping/HarfBuzzFace.cpp
[modify] https://crrev.com/c0ce7ee036e8b06de2d64bf1e91c00dedf63e447/third_party/WebKit/Source/platform/fonts/shaping/HarfBuzzFace.h
[modify] https://crrev.com/c0ce7ee036e8b06de2d64bf1e91c00dedf63e447/third_party/WebKit/Source/platform/fonts/shaping/HarfBuzzFontCache.h
[modify] https://crrev.com/c0ce7ee036e8b06de2d64bf1e91c00dedf63e447/third_party/WebKit/Source/platform/fonts/shaping/HarfBuzzShaper.cpp

Graphs have recovered, marking as fixed.