common.gypi: When clang=1 on Windows, set CC to clang-cl

(See https://code.google.com/p/gyp/source/detail?r=1846 for
how GYP deals with this.)

BUG=82385

Review URL: https://codereview.chromium.org/147083011

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@247586 0039d316-1c4b-4281-b951-d872f2087c98
Add some histograms for <a ping> requests.

So we can see if we're hitting the timeout, how long requests take, etc.

BUG=302816

Review URL: https://codereview.chromium.org/148573002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@247587 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 247586
SVN changes up to revision 247587