Increase new content rendering timeout

Increase new content rendering timeout

Due to the Mac graphics bug 537296, when the rendering timeout fires
on Mac it causes graphic artifacts to appear instead of a white screen.
When it occasionally fires simply because the initial rendering of a
page is taking too long, this causes a brief display of the wrong
content before the correct compositor frame arrives.

This CL extends the timeout from 2 seconds to 4, which we hope will prevent
the effects of bug 537296 from manifesting to users, or at least significantly reduce its prevalence, while not
compromising the purpose of the timeout. The display bug will still need to be fixed independently to properly deal with the problem.

BUG=540653
R=creis@chromium.org

Review URL: https://codereview.chromium.org/1416673002

Cr-Commit-Position: refs/heads/master@{#354798}
(cherry picked from commit 00bb4a294d0c4f567dfa60b3222b00a428e63907)

Committed: https://chromium.googlesource.com/chromium/src/+/f4ad85d26d87872df049991c64e2025bb8c1bfb7

[kenrb, 2015-11-16 16:14:14]

Committed patchset #1 (id:1) manually as
f4ad85d26d87872df049991c64e2025bb8c1bfb7.