Add Mojo API for Blink hit testing

content/browser/site_per_process_browsertest.cc

Index: content/browser/site_per_process_browsertest.cc
diff --git a/content/browser/site_per_process_browsertest.cc b/content/browser/site_per_process_browsertest.cc
index cec49d10b14e21cb81a0770112e4e706217ae3ee..5cfd6de398def4df44680fe8499e8f3283bd130e 100644
--- a/content/browser/site_per_process_browsertest.cc
+++ b/content/browser/site_per_process_browsertest.cc
@@ -273,6 +273,14 @@ double GetPageScaleFactor(Shell* shell) {
       .page_scale_factor;
 }
 
+bool callback_received = false;
+int received_frame_id = -2;
+
+void callback(int frame_id) {
+  received_frame_id = frame_id;
+  callback_received = true;
+}
+
 // Helper function that performs a surface hittest.
 void SurfaceHitTestTestHelper(
     Shell* shell,
@@ -330,6 +338,18 @@ void SurfaceHitTestTestHelper(
   child_event.click_count = 1;
   main_frame_monitor.ResetEventReceived();
   child_frame_monitor.ResetEventReceived();
+
+  callback_received = false;
+  root->current_frame_host()->GetFrameInputHandler()->HitTestFrameAt(
+      (gfx::PointF)child_event.PositionInWidget(), base::Bind(&callback));
+  while (!callback_received) {
+    base::RunLoop run_loop;
+    base::ThreadTaskRunnerHandle::Get()->PostDelayedTask(
+        FROM_HERE, run_loop.QuitClosure(), TestTimeouts::tiny_timeout());
+    run_loop.Run();
+  }
+  ASSERT_EQ(4, received_frame_id);
+
   router->RouteMouseEvent(root_view, &child_event, ui::LatencyInfo());
 
   EXPECT_TRUE(child_frame_monitor.EventWasReceived());