Setting Accurate ScrollResult from Blink for Elastic Scroll.

content/renderer/render_widget.cc

Index: content/renderer/render_widget.cc
diff --git a/content/renderer/render_widget.cc b/content/renderer/render_widget.cc
index ff314be36cba567af9beb0eb5d1a0de4e4ca688f..9509f5168fb48ddb19a0dc93e53f2b72254107ac 100644
--- a/content/renderer/render_widget.cc
+++ b/content/renderer/render_widget.cc
@@ -2147,6 +2147,12 @@ bool RenderWidget::DoesRecordFullLayer() const {
 }
 #endif
 
+#if defined(OS_MACOSX) && !defined(OS_IOS)
+bool RenderWidget::IsElasticOverscrollEnabled() const {
+  return compositor_deps_->IsElasticOverscrollEnabled();
+}
+#endif
+
 bool RenderWidget::CanComposeInline() {
   return true;
 }
@@ -2215,6 +2221,12 @@ void RenderWidget::didOverscroll(
     const blink::WebFloatSize& accumulatedRootOverScroll,
     const blink::WebFloatPoint& position,
     const blink::WebFloatSize& velocity) {
+  if (compositor_deps_->IsElasticOverscrollEnabled()) {
+    unused_delta_on_wheel_overscroll_ =
+        gfx::Vector2dF(-unusedDelta.width, -unusedDelta.height);
+    return;
+  }
+
   DidOverscrollParams params;
   // TODO(jdduke): Consider bundling the overscroll with the input event ack to
   // save an IPC.
@@ -2289,19 +2301,13 @@ void RenderWidget::ObserveWheelEventAndResult(
   if (!compositor_deps_->IsElasticOverscrollEnabled())

[jdduke (slow), 2015/06/25 23:55:45]

With https://codereview.chromium.org/1209043002/, you should be able to pass a
DidOverscrollParams* (optional) value into this function using
|event_overscroll.get()|. Then you can populate the scroll results depending on
those values.

     return;
 
-  // Blink does not accurately compute scroll bubbling or overscroll. For now,
-  // assume that an unprocessed event was entirely an overscroll, and that a
-  // processed event was entirely scroll.
-  // TODO(ccameron): Retrieve an accurate scroll result from Blink.
-  // http://crbug.com/442859
   cc::InputHandlerScrollResult scroll_result;
-  if (event_processed) {
-    scroll_result.did_scroll = true;
-  } else {
-    scroll_result.did_overscroll_root = true;
-    scroll_result.unused_scroll_delta =
-        gfx::Vector2dF(-wheel_event.deltaX, -wheel_event.deltaY);
-  }
+  scroll_result.did_scroll = event_processed;
+  scroll_result.did_overscroll_root =
+      !unused_delta_on_wheel_overscroll_.IsZero();
+  scroll_result.unused_scroll_delta = unused_delta_on_wheel_overscroll_;
+  unused_delta_on_wheel_overscroll_.set_x(0);
+  unused_delta_on_wheel_overscroll_.set_y(0);
 
   RenderThreadImpl* render_thread = RenderThreadImpl::current();
   InputHandlerManager* input_handler_manager =