Added default optional video constraints googCpuOveruseDetection and googLeakyBucket

BUG=None
TEST=Manual
NOTRY=TRUE

Review URL: https://codereview.chromium.org/84723004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@237066 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 237066