Plumb smooth scrolling in Chromium compositor

content/public/android/java/src/org/chromium/content/browser/ContentViewCore.java

Index: content/public/android/java/src/org/chromium/content/browser/ContentViewCore.java
diff --git a/content/public/android/java/src/org/chromium/content/browser/ContentViewCore.java b/content/public/android/java/src/org/chromium/content/browser/ContentViewCore.java
index ead6ba459e355e9c4d9937c9a7076f2ecd0b1be1..7682956364a78aa368d5586dd50550cd24977be2 100644
--- a/content/public/android/java/src/org/chromium/content/browser/ContentViewCore.java
+++ b/content/public/android/java/src/org/chromium/content/browser/ContentViewCore.java
@@ -1245,8 +1245,7 @@ public class ContentViewCore implements
     }
 
     public boolean isScrollInProgress() {
-        return mTouchScrollInProgress || mPotentiallyActiveFlingCount > 0
-                || getContentViewClient().isExternalScrollActive();
+        return mTouchScrollInProgress || mPotentiallyActiveFlingCount > 0;

[jdduke (slow), 2015/07/27 17:15:38]

Hmm... it's a little unfortunate to lose the accounting here for the new scroll
cases, as we won't be reusing the fling architecture :(.

In practice there will be a few minor side effects:
1) the selection handles will remain visible/janky while the smooth scroll
occurs
2) tap suppression won't work if the user taps the screen while the smooth
scroll is active.

We have the same problems with the double-tap zoom animation, so it's not the
end of the world.

[hush (inactive), 2015/07/28 00:10:43]

yeah.. I guess the same set of problems apply to "FindInPage" use case. 

[aelias_OOO_until_Jul13, 2015/07/30 02:49:33]

Well, as you say it's the same problem with double-tap zoom, and the bugs are
probably more impactful there.  These issues could probably be fixed since CC is
aware of page scale animation.

     }
 
     @SuppressWarnings("unused")
@@ -1355,6 +1354,10 @@ public class ContentViewCore implements
         nativeFlingStart(mNativeContentViewCore, timeMs, 0, 0, velocityX, velocityY, true);
     }
 
+    public void smoothScroll(int targetX, int targetY, long durationMs) {
+        mWebContents.smoothScroll(targetX, targetY, durationMs);
+    }
+
     /**
      * Cancel any fling gestures active.
      * @param timeMs Current time (in milliseconds).
@@ -1396,9 +1399,6 @@ public class ContentViewCore implements
                             computeVerticalScrollOffset(),
                             computeVerticalScrollExtent());
                     break;
-                case GestureEventType.FLING_CANCEL:
-                    listener.onFlingCancelGesture();
-                    break;
                 case GestureEventType.SCROLL_START:
                     listener.onScrollStarted(
                             computeVerticalScrollOffset(),