Add synthetic delay testing framework

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=307841,324057

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

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@242947 0039d316-1c4b-4281-b951-d872f2087c98