More refactoring for WebPlugin.

      This CL eliminates direct calls to WebPluginDelegate::DidFinishLoadWithReason
from WebFrameLoaderClient.

This CL also moves WebDataSourceImpl into webkit/api/src.  That change was
needed so that WebPluginContainerImpl can add a WebPluginLoadObserver to it,
which WebFrameLoaderClient uses to communicate back to the WebPlugin upon
completion of the frame load.

WebViewDelegate::DidFinishLoadWithReason is modified to include url and
notify_data parameters, eliminating the URLRequestRouted method.  This is done
so that we can support overlapping NPN_GetURLNotify targetting different
frames.

WebPluginContainer grows an executeScriptURL method to deal with javascript:
URLs.

NOTE: I'm working on some UI tests to better cover the case of overlapping
NPN_GetURLNotify calls.

R=jam
BUG=10036
TEST=none yet

Review URL: http://codereview.chromium.org/174514

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@24655 0039d316-1c4b-4281-b951-d872f2087c98