Make it possible to synthesize a viewport scroll

When targetViewport is true, skip the hit test and always
scroll the viewport layer.
This is to support the WebView#flingScroll API, which has been
implemented to always target at viewport scroll layer.

Accompanying blink change that adds 'targetViewport':
https://codereview.chromium.org/1187633003/

BUG=493765
CQ_INCLUDE_TRYBOTS=tryserver.blink:linux_blink_rel

Review URL: https://codereview.chromium.org/1189603004

Cr-Commit-Position: refs/heads/master@{#335750}

2 files changed, 33 insertions, 5 deletions

diff --git a/content/renderer/input/input_handler_proxy.cc b/content/renderer/input/input_handler_proxy.cc
index e8e8f37..232d8b7 100644
--- a/content/renderer/input/input_handler_proxy.cc
+++ b/content/renderer/input/input_handler_proxy.cc
@@ -426,8 +426,14 @@ InputHandlerProxy::EventDisposition InputHandlerProxy::HandleGestureScrollBegin(
   DCHECK(!expect_scroll_update_end_);
   expect_scroll_update_end_ = true;
 #endif
-  cc::InputHandler::ScrollStatus scroll_status = input_handler_->ScrollBegin(
-      gfx::Point(gesture_event.x, gesture_event.y), cc::InputHandler::GESTURE);
+  cc::InputHandler::ScrollStatus scroll_status;
+  if (gesture_event.data.scrollBegin.targetViewport) {
+    scroll_status = input_handler_->RootScrollBegin(cc::InputHandler::GESTURE);
+  } else {
+    scroll_status = input_handler_->ScrollBegin(
+        gfx::Point(gesture_event.x, gesture_event.y),
+        cc::InputHandler::GESTURE);
+  }
   UMA_HISTOGRAM_ENUMERATION("Renderer4.CompositorScrollHitTestResult",
                             scroll_status,
                             cc::InputHandler::ScrollStatusCount);
@@ -487,9 +493,14 @@ InputHandlerProxy::EventDisposition InputHandlerProxy::HandleGestureFlingStart(
   cc::InputHandler::ScrollStatus scroll_status;
 
   if (gesture_event.sourceDevice == blink::WebGestureDeviceTouchpad) {
-    scroll_status = input_handler_->ScrollBegin(
-        gfx::Point(gesture_event.x, gesture_event.y),
-        cc::InputHandler::NON_BUBBLING_GESTURE);
+    if (gesture_event.data.flingStart.targetViewport) {
+      scroll_status = input_handler_->RootScrollBegin(
+          cc::InputHandler::NON_BUBBLING_GESTURE);
+    } else {
+      scroll_status = input_handler_->ScrollBegin(
+          gfx::Point(gesture_event.x, gesture_event.y),
+          cc::InputHandler::NON_BUBBLING_GESTURE);
+    }
   } else {
     if (!gesture_scroll_on_impl_thread_)
       scroll_status = cc::InputHandler::SCROLL_ON_MAIN_THREAD;
diff --git a/content/renderer/input/input_handler_proxy_unittest.cc b/content/renderer/input/input_handler_proxy_unittest.cc
index a1a55f2..0bfe1e2 100644
--- a/content/renderer/input/input_handler_proxy_unittest.cc
+++ b/content/renderer/input/input_handler_proxy_unittest.cc
@@ -87,6 +87,8 @@ class MockInputHandler : public cc::InputHandler {
   MOCK_METHOD2(ScrollBegin,
                ScrollStatus(const gfx::Point& viewport_point,
                             cc::InputHandler::ScrollInputType type));
+  MOCK_METHOD1(RootScrollBegin,
+               ScrollStatus(cc::InputHandler::ScrollInputType type));
   MOCK_METHOD2(ScrollAnimated,
                ScrollStatus(const gfx::Point& viewport_point,
                             const gfx::Vector2dF& scroll_delta));
@@ -395,6 +397,21 @@ TEST_F(InputHandlerProxyTest, GestureScrollIgnored) {
   VERIFY_AND_RESET_MOCKS();
 }
 
+TEST_F(InputHandlerProxyTest, GestureScrollBeginThatTargetViewport) {
+  // We shouldn't send any events to the widget for this gesture.
+  expected_disposition_ = InputHandlerProxy::DID_HANDLE;
+  VERIFY_AND_RESET_MOCKS();
+
+  EXPECT_CALL(mock_input_handler_, RootScrollBegin(testing::_))
+      .WillOnce(testing::Return(cc::InputHandler::SCROLL_STARTED));
+
+  gesture_.type = WebInputEvent::GestureScrollBegin;
+  gesture_.data.scrollBegin.targetViewport = true;
+  EXPECT_EQ(expected_disposition_, input_handler_->HandleInputEvent(gesture_));
+
+  VERIFY_AND_RESET_MOCKS();
+}
+
 TEST_F(InputHandlerProxyTest, GesturePinch) {
   // We shouldn't send any events to the widget for this gesture.
   expected_disposition_ = InputHandlerProxy::DID_HANDLE;