Move CancelableTaskTracker to //base/task/CancelableTaskTracker.

CancelableTaskTracker is used by //chrome code that is due to componentized.
This CL moves the class to //base/task and wraps it in the ::base::task namespace.

BUG=335135
TBR=thakis

Review URL: https://codereview.chromium.org/137263007

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@249397 0039d316-1c4b-4281-b951-d872f2087c98
Back CAOpenGLLayers by CGL contexts instead of NSGL contexts

Change CompositingIOSurfaceContext to have a separate path
for creating a CGLContextObj directly, rather than creating a
NSOpenGLContext and using its CGLContextObj. Add asserts
to prevent trying to grab the NSOpenGLContext when using
CoreAnimation.

Change the CAOpenGLLayer to create the CGLContextObj at
creation, and pass a retained pointer to it and its pixel format
when requested, and allow the superclass to handle the release
of the pixel format and context. This matches the behavior in
WebKit.

Change DisplayLinkMac to call CVDisplayLinkRelease instead
of CFRelease because here is no documentation that CFRelease
may be used with a CVDisplayLink.

BUG=245900

Review URL: https://codereview.chromium.org/131453012

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@249398 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 249398