Remove WGC3DCBImpl::GetGPUProcessID()

It's used for blocking renders that are trying to create
 a context after the GPU process crashed through comparing
 gpu process IDs.

Remove this code as we can handle SwapCompositorFrame
 more gracefully nowadays after resources were lost.
 But still fail renderer view context creation when
 gpu browser compositing gets turned off.

BUG=270179,329737

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=241425

R=danakj@chromium.org, palmer@chromium.org, piman@chromium.org

Review URL: https://codereview.chromium.org/111063003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@244950 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 244950