Disable memory metrics in media benchmarks.

Memory metrics as is do not add value to media benchmarks since they
count for all the memory used by the browser/renderer since starting a
test and not measuring media specific memory usage.

BUG=324951

Review URL: https://codereview.chromium.org/179053003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@253767 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 253767