Add histograms for tracking truncated QUIC ACK frames.

Review URL: https://codereview.chromium.org/124013002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@242988 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 242988
Valgrind: Suppress a flaky test-only memory leak in ExtensionActionIconFactoryTest.

BUG=298788
TBR=vabr@chromium.org
NOTRY=true

Review URL: https://codereview.chromium.org/124383002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@242989 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 242989