Add synthetic delay points for latency testing

Add synthetic delay points for simulating long computation in the
following parts of the graphics/input pipeline:

1. blink.HandleInputEvent - Expensive JavaScript input event handling.
2. cc.RasterRequiredForActivation - Long running raster tasks.
3. cc.BeginMainFrame - Complex main thread picture recording, layout or
   rAF.
4. gpu.AsyncTexImage - Slow texture uploads.
5. gpu.SwapBuffers - GPU-bound rendering.

BUG=307841

Review URL: https://codereview.chromium.org/83183005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@244175 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 244175