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/drag_handler_ctocpp.cc

@@ -9,12 +9,13 @@
 // implementations. See the translator.README.txt file in the tools directory
 // for more information.
 //
-// $hash=c8a4667e566076b36af39a83ba15cb1015821da9$
+// $hash=ed9ec27e4e93df6821437ee0d49da3ebd122bed3$
 //
 
 #include "libcef_dll/ctocpp/drag_handler_ctocpp.h"
 #include "libcef_dll/cpptoc/browser_cpptoc.h"
 #include "libcef_dll/cpptoc/drag_data_cpptoc.h"
+#include "libcef_dll/cpptoc/frame_cpptoc.h"
 #include "libcef_dll/shutdown_checker.h"
 
 // VIRTUAL METHODS - Body may be edited by hand.
@@ -51,6 +52,7 @@ bool CefDragHandlerCToCpp::OnDragEnter(CefRefPtr<CefBrowser> browser,
 NO_SANITIZE("cfi-icall")
 void CefDragHandlerCToCpp::OnDraggableRegionsChanged(
     CefRefPtr<CefBrowser> browser,
+    CefRefPtr<CefFrame> frame,
     const std::vector<CefDraggableRegion>& regions) {
   shutdown_checker::AssertNotShutdown();
 
@@ -64,6 +66,10 @@ void CefDragHandlerCToCpp::OnDraggableRegionsChanged(
   DCHECK(browser.get());
   if (!browser.get())
     return;
+  // Verify param: frame; type: refptr_diff
+  DCHECK(frame.get());
+  if (!frame.get())
+    return;
 
   // Translate param: regions; type: simple_vec_byref_const
   const size_t regionsCount = regions.size();
@@ -80,7 +86,8 @@ void CefDragHandlerCToCpp::OnDraggableRegionsChanged(
 
   // Execute
   _struct->on_draggable_regions_changed(
-      _struct, CefBrowserCppToC::Wrap(browser), regionsCount, regionsList);
+      _struct, CefBrowserCppToC::Wrap(browser), CefFrameCppToC::Wrap(frame),
+      regionsCount, regionsList);
 
   // Restore param:regions; type: simple_vec_byref_const
   if (regionsList)