Handle startup urls pref migration during master_prefs import.

This will cause master_prefs files that contain the old name for the
startup urls pref to have the new name added during import time iff
the new name doesn't already exist.

BUG=299290
TEST=First run with a master prefs file that contains session.urls_to_restore_on_startup. Observe that the value is respected.

Review URL: https://codereview.chromium.org/52603005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@232348 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 232348
cc: Fix PicturePile clearing for non-origin canvases

When canvases are larger than content, and content is stretched and
terminates on a non-integer pixel boundary, then the area underneath
that content must be cleared first.  The clearing code attempted to
clear a 2 pixel wide strip, but was not translating it, so it only
worked for canvases located at the origin.

R=brianderson@chromium.org
BUG=296672

Review URL: https://codereview.chromium.org/51433003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@232349 0039d316-1c4b-4281-b951-d872f2087c98
flip test
Make sure that the "vertical flip" parameter in gl_helper* is tested properly.

BUG=313477

Review URL: https://codereview.chromium.org/51863004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@232350 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 232350