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.

include/capi/cef_browser_capi.h

@@ -33,7 +33,7 @@
 // by hand. See the translator.README.txt file in the tools directory for
 // more information.
 //
-// $hash=2385e0531c91a419fe7f4036b5a59da743b1622e$
+// $hash=623d324a1ef5637353ae74761fdc04eac4d99716$
 //
 
 #ifndef CEF_INCLUDE_CAPI_CEF_BROWSER_CAPI_H_
@@ -45,7 +45,6 @@
 #include "include/capi/cef_frame_capi.h"
 #include "include/capi/cef_image_capi.h"
 #include "include/capi/cef_navigation_entry_capi.h"
-#include "include/capi/cef_process_message_capi.h"
 #include "include/capi/cef_request_context_capi.h"
 
 #ifdef __cplusplus
@@ -179,15 +178,6 @@ typedef struct _cef_browser_t {
   ///
   void(CEF_CALLBACK* get_frame_names)(struct _cef_browser_t* self,
                                       cef_string_list_t names);
-
-  ///
-  // Send a message to the specified |target_process|. Returns true (1) if the
-  // message was sent successfully.
-  ///
-  int(CEF_CALLBACK* send_process_message)(
-      struct _cef_browser_t* self,
-      cef_process_id_t target_process,
-      struct _cef_process_message_t* message);
 } cef_browser_t;
 
 ///