Rename BeginFrame to BeginMainFrame and BeginImplFrame (part 3).

Third patch in a series to rename BeginFrame. This patch focuses on
cc::ThreadProxy, cc::LayerTreeHost, cc::LayerTreeHostImpl, cc::OutputSurface
and it's related (sub)classes.

In the scheduler, the term 'BeginFrame' is used for both the main thread and the
impl thread. This can cause confusion if it's not obvious which one is being
refered to. To clarify this, we rename BeginFrame to BeginMainFrame and
BeginImplFrame, respectively.

BUG=261765

Review URL: https://codereview.chromium.org/35023002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@230453 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 230453
Disable ClientSideDetectionHostTest.OnPhishingDetectionDoneDisabled which fails on Blink Vista

BUG=299149
TBR=noelutz
NOTRY=true

Review URL: https://codereview.chromium.org/37523002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@230454 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 230454