[Autofill] Migrate ContentAutofillDriver<-->AutofillAgent IPCs to mojo.

content/browser/frame_host/render_frame_host_impl.cc

Index: content/browser/frame_host/render_frame_host_impl.cc
diff --git a/content/browser/frame_host/render_frame_host_impl.cc b/content/browser/frame_host/render_frame_host_impl.cc
index fadeeca42041cb03120150ffe39978fa7c35804d..ee28ece633ca3ea5454cf9713b5d80969d0af936 100644
--- a/content/browser/frame_host/render_frame_host_impl.cc
+++ b/content/browser/frame_host/render_frame_host_impl.cc
@@ -2394,8 +2394,14 @@ void RenderFrameHostImpl::SetUpMojoIfNeeded() {
     return;
 
   interface_registry_.reset(new shell::InterfaceRegistry(nullptr));
-  if (!GetProcess()->GetRemoteInterfaces())
+
+  // The RenderProcessHost may not have remote interfaces in some test
+  // environments. In that case we create an empty InterfaceProvider so tests
+  // can register mock implementations.

[dcheng, 2016/07/12 14:22:13]

Can we fix the test harness (ChromeRenderViewTest, I assume?) to just set this
up correctly? I'd rather limit the test-specific code to tests.

[leonhsl(Using Gerrit), 2016/07/13 03:48:31]

I think even we change ChromeRenderViewTest and some other test harness, we
still can't avoid adding some logic into RenderProcessHostImpl to access the
|remote_interfaces_|. And, seems Ben and Ken are working for some big changes
for content layer {InterfaceProvider,InterfaceRegistry}, so later maybe the
problem will disappear or we have to go a different way here. So I don't think
current solution is unacceptable.

[dcheng, 2016/07/14 04:31:44]

To help me understand better, which tests were failing without this?

[leonhsl(Using Gerrit), 2016/07/14 09:57:31]

I encountered the problem in
https://codereview.chromium.org/2007473004/diff/300001/components/autofill/co...
Line267, where I found the |remote_interfaces_| of main render frame host is
always nullptr. 

[dcheng, 2016/07/19 14:34:11]

I think we just need to set an InterfaceProvider for the MockRenderProcesHost's
interface registry to make this work, right? See
https://cs.chromium.org/chromium/src/content/public/test/mock_render_process_...

[leonhsl(Using Gerrit), 2016/07/20 03:01:07]

Which on do you mean?
  1, Initialize MockRenderProcesHost class with an empty InterfaceProvider;
  2, Set an empty InterfaceProvider for MockRenderProcesHost only for this test
case.

Actually I don't understand why we must avoid initializing an empty
InterfaceProvider for RFHI, this behavior aligns with before(When we were using
ServiceRegistry).

+  if (!GetProcess()->GetRemoteInterfaces()) {
+    remote_interfaces_.reset(new shell::InterfaceProvider);
     return;
+  }
 
   RegisterMojoInterfaces();
   mojom::FrameFactoryPtr frame_factory;