Make the global render thread object a regular global object rather than a
special TLS value. This is slightly faster for this commonly-used function, and
we don't ever have more than one (it's like this because we were originally
planning on having more than one RenderThread).

BUG=5635
Review URL: http://codereview.chromium.org/15052

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@7272 0039d316-1c4b-4281-b951-d872f2087c98
8 files changed