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/renderer/render_frame_util.cc

@@ -5,9 +5,11 @@
 
 #include "libcef/renderer/render_frame_util.h"
 
+#include "libcef/common/frame_util.h"
 #include "libcef/renderer/blink_glue.h"
 
 #include "base/logging.h"
+#include "content/public/renderer/render_view.h"
 #include "content/renderer/render_frame_impl.h"
 #include "third_party/blink/public/web/web_local_frame.h"
 
@@ -18,17 +20,16 @@ int64_t GetIdentifier(blink::WebLocalFrame* frame) {
   // routing IDs are unique within a given renderer process.
   content::RenderFrame* render_frame =
       content::RenderFrame::FromWebFrame(frame);
-  DCHECK(render_frame);
-  if (render_frame)
-    return render_frame->GetRoutingID();
-  return blink_glue::kInvalidFrameId;
+  return frame_util::MakeFrameId(render_frame->GetRenderView()->GetRoutingID(),
+                                 render_frame->GetRoutingID());
 }
 
 std::string GetName(blink::WebLocalFrame* frame) {
   DCHECK(frame);
   // Return the assigned name if it is non-empty. This represents the name
   // property on the frame DOM element. If the assigned name is empty, revert to
-  // the internal unique name.
+  // the internal unique name. This matches the logic in
+  // CefFrameHostImpl::RefreshAttributes.
   if (frame->AssignedName().length() > 0) {
     return frame->AssignedName().Utf8();
   }