Unify Android Webview and Chrome's fling

android_webview/browser/browser_view_renderer.cc

Index: android_webview/browser/browser_view_renderer.cc
diff --git a/android_webview/browser/browser_view_renderer.cc b/android_webview/browser/browser_view_renderer.cc
index b9336d6119a230f9ccef7ac87c39bad71015c35d..ab3bc84822536ed11dbf78f6961d0454e4e97a6d 100644
--- a/android_webview/browser/browser_view_renderer.cc
+++ b/android_webview/browser/browser_view_renderer.cc
@@ -414,6 +414,12 @@ void BrowserViewRenderer::OnDetachedFromWindow() {
   UpdateCompositorIsActive();
 }
 
+void BrowserViewRenderer::OnComputeScroll(base::TimeTicks animation_time) {
+  if (pending_fling_animation_.is_null())
+    return;
+  FlushPendingFlingAnimation(animation_time);
+}
+
 void BrowserViewRenderer::ReleaseHardware() {
   DCHECK(hardware_enabled_);
   ReturnUnusedResource(shared_renderer_state_.PassUncommittedFrameOnUI());
@@ -605,6 +611,13 @@ BrowserViewRenderer::RootLayerStateAsValue(
   return state;
 }
 
+void BrowserViewRenderer::SetNeedsAnimateFling(
+    const AnimationCallback& fling_animation) {
+  // TODO(jdduke): Skip invalidate if animation already pending?
+  pending_fling_animation_ = fling_animation;
+  client_->PostInvalidate();
+}
+
 void BrowserViewRenderer::DidOverscroll(gfx::Vector2dF accumulated_overscroll,
                                         gfx::Vector2dF latest_overscroll_delta,
                                         gfx::Vector2dF current_fling_velocity) {
@@ -617,7 +630,19 @@ void BrowserViewRenderer::DidOverscroll(gfx::Vector2dF accumulated_overscroll,
       scaled_overscroll_delta + overscroll_rounding_error_);
   overscroll_rounding_error_ =
       scaled_overscroll_delta - rounded_overscroll_delta;
-  client_->DidOverscroll(rounded_overscroll_delta);
+
+  gfx::Vector2dF fling_velocity_pixels =
+      gfx::ScaleVector2d(current_fling_velocity, physical_pixel_scale);
+
+  const bool first_overscroll_x =
+      accumulated_overscroll.x() &&
+      accumulated_overscroll.x() == latest_overscroll_delta.x();
+  const bool first_overscroll_y =
+      accumulated_overscroll.y() &&
+      accumulated_overscroll.y() == latest_overscroll_delta.y();
+
+  client_->DidOverscroll(rounded_overscroll_delta, fling_velocity_pixels,
+                         first_overscroll_x, first_overscroll_y);
 }
 
 void BrowserViewRenderer::PostInvalidate() {
@@ -694,6 +719,16 @@ void BrowserViewRenderer::ForceFakeCompositeSW() {
   CompositeSW(&canvas);
 }
 
+void BrowserViewRenderer::FlushPendingFlingAnimation(
+    base::TimeTicks animation_time) {
+  TRACE_EVENT0("android_webview",
+               "BrowserViewRenderer::FlushPendingFlingAnimation");
+  DCHECK(!pending_fling_animation_.is_null());
+  AnimationCallback animation = pending_fling_animation_;
+  pending_fling_animation_.Reset();
+  animation.Run(animation_time);
+}
+
 bool BrowserViewRenderer::CompositeSW(SkCanvas* canvas) {
   DCHECK(compositor_);
   CancelFallbackTick();