Add optional browser metrics (cpu, memory) to media measurements.

With "add_browser_metrics" options, the media measurements will record
memory and cpu metrics per test.

BUG=280326

Review URL: https://codereview.chromium.org/25084004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@228083 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 228083