Add Dependency.processed and .hooks_ran to ease debugging.

Accept when more than one reference exist for FromImpl(), it may happen as it is the case for pagespeed.

Not much behavior change.

Review URL: http://codereview.chromium.org/3126003

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@55575 0039d316-1c4b-4281-b951-d872f2087c98