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/cpptoc/drag_handler_cpptoc.cc

@@ -9,12 +9,13 @@
 // implementations. See the translator.README.txt file in the tools directory
 // for more information.
 //
-// $hash=c85e942b6518aa3951dbd47b3ff1097f4a6f88fa$
+// $hash=9c1c7a83aab83ba8cdb751db09373aaa49601ded$
 //
 
 #include "libcef_dll/cpptoc/drag_handler_cpptoc.h"
 #include "libcef_dll/ctocpp/browser_ctocpp.h"
 #include "libcef_dll/ctocpp/drag_data_ctocpp.h"
+#include "libcef_dll/ctocpp/frame_ctocpp.h"
 #include "libcef_dll/shutdown_checker.h"
 
 namespace {
@@ -52,6 +53,7 @@ int CEF_CALLBACK drag_handler_on_drag_enter(struct _cef_drag_handler_t* self,
 void CEF_CALLBACK drag_handler_on_draggable_regions_changed(
     struct _cef_drag_handler_t* self,
     cef_browser_t* browser,
+    struct _cef_frame_t* frame,
     size_t regionsCount,
     cef_draggable_region_t const* regions) {
   shutdown_checker::AssertNotShutdown();
@@ -65,6 +67,10 @@ void CEF_CALLBACK drag_handler_on_draggable_regions_changed(
   DCHECK(browser);
   if (!browser)
     return;
+  // Verify param: frame; type: refptr_diff
+  DCHECK(frame);
+  if (!frame)
+    return;
   // Verify param: regions; type: simple_vec_byref_const
   DCHECK(regionsCount == 0 || regions);
   if (regionsCount > 0 && !regions)
@@ -81,7 +87,8 @@ void CEF_CALLBACK drag_handler_on_draggable_regions_changed(
 
   // Execute
   CefDragHandlerCppToC::Get(self)->OnDraggableRegionsChanged(
-      CefBrowserCToCpp::Wrap(browser), regionsList);
+      CefBrowserCToCpp::Wrap(browser), CefFrameCToCpp::Wrap(frame),
+      regionsList);
 }
 
 }  // namespace