Support reconnect of the mojo frame channel (fixes issue #3260)

The mojo channel used for frame communication may disconnect for a variety of
reasons including frame navigation, frame destruction, or insertion into the
BackForwardCache (when the browser-side frame representation is destroyed and
closes the connection). When disconnect occurs we now evaluate the situation
and reconnect if appropriate.

Connections are now initiated solely from the renderer process and the
RenderFrame is passed as an argument to FrameAttached() instead of being
retrieved independently. Messages are queued while the frame is disconnected
and sent only after FrameAttachedAck() is received from the browser process.
The renderer process will be crashed intentionally with a "connection retry
failure" message if the reconnect fails 3 times in a row.

libcef/browser/browser_info.cc

@@ -168,10 +168,13 @@ void CefBrowserInfo::FrameHostStateChanged(
            content::RenderFrameHost::LifecycleState::kInBackForwardCache) &&
       new_state == content::RenderFrameHost::LifecycleState::kActive) {
     if (auto frame = GetFrameForHost(host)) {
+      // Should only occur for the main frame.
+      CHECK(frame->IsMain());
+
       // Update the associated RFH, which may have changed.
       frame->MaybeReAttach(this, host);
 
-      if (frame->IsMain()) {
+      {
         // Update the main frame object.
         NotificationStateLock lock_scope(this);
         SetMainFrame(browser_, frame);