Plumb smooth scrolling in Chromium compositor

content/browser/android/content_view_core_impl.cc

 // Copyright 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/browser/android/content_view_core_impl.h"
 
 #include "base/android/jni_android.h"
 #include "base/android/jni_array.h"
 #include "base/android/jni_string.h"
 #include "base/android/scoped_java_ref.h"
@@ skipping 1048 matching lines @@
 }
 
 void ContentViewCoreImpl::FlingCancel(JNIEnv* env, jobject obj, jlong time_ms) {
   WebGestureEvent event = MakeGestureEvent(
       WebInputEvent::GestureFlingCancel, time_ms, 0, 0);
   event.data.flingCancel.preventBoosting = true;
 
   SendGestureEvent(event);
 }
 
+void ContentViewCoreImpl::SmoothScrollStart(JNIEnv* env,
+                                            jobject obj,
+                                            jlong time_ms,
+                                            float start_x,
+                                            float start_y,
+                                            float dx,
+                                            float dy,
+                                            jlong duration_ms) {
+  WebGestureEvent event = MakeGestureEvent(WebInputEvent::GestureFlingStart,
+                                           time_ms, start_x, start_y);
+  event.data.flingStart.isSmoothScroll = true;
+  event.data.flingStart.dx = dx / dpi_scale();
+  event.data.flingStart.dy = dy / dpi_scale();
+  event.data.flingStart.durationMs = duration_ms;
+  event.data.flingStart.targetViewport = true;
+
+  // Velocities are not used for computing the smooth scroll animation curve.
+  // But they are included here anyways because zero-velocity fling results in
+  // GestureScrollEnd immediately.
+  event.data.flingStart.velocityX = dx / dpi_scale() / time_ms * 1000;
+  event.data.flingStart.velocityY = dy / dpi_scale() / time_ms * 1000;
+
+  SendGestureEvent(event);
+}
+
 void ContentViewCoreImpl::SingleTap(JNIEnv* env, jobject obj, jlong time_ms,
                                     jfloat x, jfloat y) {
   // Tap gestures should always be preceded by a TapDown, ensuring consistency
   // with the touch-based gesture detection pipeline.
   WebGestureEvent tap_down_event = MakeGestureEvent(
       WebInputEvent::GestureTapDown, time_ms, x, y);
   tap_down_event.data.tap.tapCount = 1;
   SendGestureEvent(tap_down_event);
 
   WebGestureEvent tap_event = MakeGestureEvent(
@@ skipping 397 matching lines @@
     return NULL;
 
   return view->GetJavaObject().Release();
 }
 
 bool RegisterContentViewCore(JNIEnv* env) {
   return RegisterNativesImpl(env);
 }
 
 }  // namespace content