Add WebFrameClient::cancelledError to avoid a dependency on

      the net/ module.

This CL also tweaks some existing WebFrameClient methods:
1) to ensure that they have a WebFrame pointer for context
2) to rename cannotShowURLError to cannotHandleRequestError
to better match the canHandleRequest method.

R=yaar
BUG=24606
TEST=none

Review URL: http://codereview.chromium.org/306011

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@29561 0039d316-1c4b-4281-b951-d872f2087c98