CC: Cache non-ideal tiles, but don't paint them.

This patch never paints _new_ non-ideal tiles. The old ones
exist only because they are still being used (the ideal
resolution hasn't covered all non-ideal tiles yet).

BUG=307206

Review URL: https://codereview.chromium.org/71753003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@236163 0039d316-1c4b-4281-b951-d872f2087c98
Remove unit_tests target from iOS builds.

chrome/ is no longer being brought up on iOS, since code used on iOS should 
be extracted into layered components. unit_tests is now empty on iOS, so stop 
building it.

BUG=312293

Review URL: https://codereview.chromium.org/72663006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@236164 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 236164