NOT FOR LANDING - [WebView] Allow fling animation via the LayerScrollOffsetDelegate

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 ea9d60312836a4a3c45dc9dd20850bf05028defd..9730bbd3a151b3680664ec815a6997636905d30c 100644
--- a/android_webview/browser/browser_view_renderer.cc
+++ b/android_webview/browser/browser_view_renderer.cc
@@ -422,6 +422,12 @@ void BrowserViewRenderer::OnDetachedFromWindow() {
   DCHECK(!hardware_enabled_);
 }
 
+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());
@@ -626,6 +632,13 @@ 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) {
@@ -638,7 +651,21 @@ 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::EnsureContinuousInvalidation(
@@ -742,6 +769,16 @@ 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_);
   ReturnResourceFromParent();