Add Mojo API for Blink hit testing

content/renderer/input/render_widget_input_handler.cc

Index: content/renderer/input/render_widget_input_handler.cc
diff --git a/content/renderer/input/render_widget_input_handler.cc b/content/renderer/input/render_widget_input_handler.cc
index 4a9261ba98a411adfa49b7a800555b06667e2a5a..b5560ba0442077c5f794e41d2e72185c16658277 100644
--- a/content/renderer/input/render_widget_input_handler.cc
+++ b/content/renderer/input/render_widget_input_handler.cc
@@ -17,6 +17,7 @@
 #include "content/common/input/input_event_ack.h"
 #include "content/common/input/input_event_ack_state.h"
 #include "content/public/common/content_switches.h"
+#include "content/public/renderer/render_frame.h"
 #include "content/renderer/gpu/render_widget_compositor.h"
 #include "content/renderer/ime_event_guard.h"
 #include "content/renderer/input/render_widget_input_handler_delegate.h"
@@ -206,6 +207,12 @@ RenderWidgetInputHandler::RenderWidgetInputHandler(
 
 RenderWidgetInputHandler::~RenderWidgetInputHandler() {}
 
+int RenderWidgetInputHandler::HitTestFrameAt(const gfx::PointF& point) {
+  return RenderFrame::GetRoutingIdForWebFrame(
+      widget_->GetWebWidget()->HitTestFrameAt(
+          blink::WebFloatPoint(point.x(), point.y())));
+}
+
 void RenderWidgetInputHandler::HandleInputEvent(
     const blink::WebCoalescedInputEvent& coalesced_event,
     const ui::LatencyInfo& latency_info,