Move message routing from CefBrowser to CefFrame (see issue #2498).

This change moves the SendProcessMessage method from CefBrowser to CefFrame and
adds CefBrowser parameters to OnProcessMessageReceived and
OnDraggableRegionsChanged.

The internal implementation has changed as follows:
- Frame IDs are now a 64-bit combination of the 32-bit render_process_id and
  render_routing_id values that uniquely identify a RenderFrameHost (RFH).
- CefFrameHostImpl objects are now managed by CefBrowserInfo with life span tied
  to RFH expectations. Specifically, a CefFrameHostImpl object representing a
  sub-frame will be created when a RenderFrame is created in the renderer
  process and detached when the associated RenderFrame is deleted or the
  renderer process in which it runs has died.
- The CefFrameHostImpl object representing the main frame will always be valid
  but the underlying RFH (and associated frame ID) may change over time as a
  result of cross-origin navigations. Despite these changes calling LoadURL on
  the main frame object in the browser process will always navigate as expected.
- Speculative RFHs, which may be created as a result of a cross-origin
  navigation and discarded if that navigation is not committed, are now handled
  correctly (e.g. ignored in most cases until they're committed).
- It is less likely, but still possible, to receive a CefFrame object with an
  invalid frame ID (ID < 0). This can happen in cases where a RFH has not yet
  been created for a sub-frame. For example, when OnBeforeBrowse is called
  before initiating navigation in a previously nonexisting sub-frame.

To test: All tests pass with NetworkService enabled and disabled.

libcef_dll/ctocpp/browser_ctocpp.h

@@ -9,7 +9,7 @@
 // implementations. See the translator.README.txt file in the tools directory
 // for more information.
 //
-// $hash=8f3cd27505fb1c95ab77ce1ca8a499eb79c0ede4$
+// $hash=af9ed3cfda9c94f046f4f9b5c9c94b1b38ff2e64$
 //
 
 #ifndef CEF_LIBCEF_DLL_CTOCPP_BROWSER_CTOCPP_H_
@@ -56,8 +56,6 @@ class CefBrowserCToCpp
   size_t GetFrameCount() OVERRIDE;
   void GetFrameIdentifiers(std::vector<int64>& identifiers) OVERRIDE;
   void GetFrameNames(std::vector<CefString>& names) OVERRIDE;
-  bool SendProcessMessage(CefProcessId target_process,
-                          CefRefPtr<CefProcessMessage> message) OVERRIDE;
 };
 
 #endif  // CEF_LIBCEF_DLL_CTOCPP_BROWSER_CTOCPP_H_