Nested pre-fling for AbsListView and ScrollView

Add nested pre-fling support to all framework widgets that currently
support nested fling.

Change-Id: Ieaf9d12938dbfeea779c2aee2f5a081c287c8e96

Author: adamp

core/java/android/widget/AbsListView.java

@@ -3857,13 +3857,17 @@ public void run() {
                                     firstChildTop == contentTop - mOverscrollDistance) ||
                               (mFirstPosition + childCount == mItemCount &&
                                     lastChildBottom == contentBottom + mOverscrollDistance))) {
-                        if (mFlingRunnable == null) {
-                            mFlingRunnable = new FlingRunnable();
+                        if (!dispatchNestedPreFling(0, -initialVelocity)) {
+                            if (mFlingRunnable == null) {
+                                mFlingRunnable = new FlingRunnable();
+                            }
+                            reportScrollStateChange(OnScrollListener.SCROLL_STATE_FLING);
+                            mFlingRunnable.start(-initialVelocity);
+                            dispatchNestedFling(0, -initialVelocity, true);
+                        } else {
+                            mTouchMode = TOUCH_MODE_REST;
+                            reportScrollStateChange(OnScrollListener.SCROLL_STATE_IDLE);
                         }
-                        reportScrollStateChange(OnScrollListener.SCROLL_STATE_FLING);
-
-                        mFlingRunnable.start(-initialVelocity);
-                        dispatchNestedFling(0, -initialVelocity, true);
                     } else {
                         mTouchMode = TOUCH_MODE_REST;
                         reportScrollStateChange(OnScrollListener.SCROLL_STATE_IDLE);
@@ -4029,7 +4033,9 @@ public boolean onNestedFling(View target, float velocityX, float velocityY, bool
             if (mFlingRunnable == null) {
                 mFlingRunnable = new FlingRunnable();
             }
-            mFlingRunnable.start((int) velocityY);
+            if (!dispatchNestedPreFling(0, velocityY)) {
+                mFlingRunnable.start((int) velocityY);
+            }
             return true;
         }
         return dispatchNestedFling(velocityX, velocityY, consumed);

core/java/android/widget/ScrollView.java

@@ -1577,9 +1577,11 @@ public void fling(int velocityY) {
     private void flingWithNestedDispatch(int velocityY) {
         final boolean canFling = (mScrollY > 0 || velocityY > 0) &&
                 (mScrollY < getScrollRange() || velocityY < 0);
-        dispatchNestedFling(0, velocityY, canFling);
-        if (canFling) {
-            fling(velocityY);
+        if (!dispatchNestedPreFling(0, velocityY)) {
+            dispatchNestedFling(0, velocityY, canFling);
+            if (canFling) {
+                fling(velocityY);
+            }
         }
     }