Render focus-selection-textarea at constant font-size to avoid flakiness

When crrev.com/453211 updated FreeType on Linux, some glyphs
got bigger due to the new antialiasing and hinting settings.

Bigger glyphs made focus-selection-textarea.html layout differently.
With the new layout, scripted mouse clicks no longer hit the right spot.

After the manual rebaselining in crrev.com/453211, the expected result
on Linux started to include FAIL whereas other platforms still expected
PASS. This CL makes also Linux PASS.

BUG=706119, 274030

TEST=python third_party/WebKit/Tools/Scripts/run-webkit-tests -t\
     PcDebug LayoutTests/fast/forms/focus-selection-textarea.html

Review-Url: https://codereview.chromium.org/2786953002
Cr-Commit-Position: refs/heads/master@{#460732}
3 files changed