Add an extension to expose some primitives to JS for doing 
benchmarking from within Chrome.  Because the JS resides
in the renderer and the HTTP logic resides in the browser,
this required creation of two new, control messages which
can be sent from the renderer to the browser.

These are controlled under a new commandline option
"--enable-benchmarking"

BUG=6754
TEST=none

Review URL: http://codereview.chromium.org/119191

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@17722 0039d316-1c4b-4281-b951-d872f2087c98
12 files changed