Include the mis-matching context along with the contexts a Feature is available
in within the message result of Feature::GetAvailabilityMessage.

BUG=b/9335685
R=mpcomplete@chromium.org

Review URL: https://codereview.chromium.org/27272002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@229232 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 229232
Add supoort for stop page loads in TabBase.

Always use the contentviewcore if present as it controls navigation
even if native pages are present.

BUG=291279
R=newt@chromium.org
NOTRY=true

Review URL: https://codereview.chromium.org/27597002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@229234 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 229234