Add synthetic delay testing framework
    
This patch introduces a synthetic delay framework for testing. It will be used to measure animation smoothness and input latency under varying loads in different parts of the graphics and input pipelines.
    
The basic building block for synthetic delays is the delay point which is inserted to a function scope of interest, e.g.:
    
    TRACE_EVENT_SYNTHETIC_DELAY("cc.DrawAndSwap");
    
Testing code can then configure how long the enclosing scope of the delay point should take to execute. If the function completes faster than the configured duration, a busy loop is used to make up the difference.
    
BUG=307841

Review URL: https://codereview.chromium.org/53923005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@237580 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 237580