Fix scroll jump in ScrollView.

If a touch event was targeted at a ScrollView child, the content would jump after
the user moved her finger by the required threshold. This is inconsistent with
ListView's behavior.

Fixes #2296622.

core/java/android/webkit/WebView.java

@@ -3990,6 +3990,13 @@ public class WebView extends AbsoluteLayout
                     }
 
                     mTouchMode = TOUCH_DRAG_MODE;
+                    mLastTouchX = x;
+                    mLastTouchY = y;
+                    fDeltaX = 0.0f;
+                    fDeltaY = 0.0f;
+                    deltaX = 0;
+                    deltaY = 0;
+
                     WebViewCore.pauseUpdate(mWebViewCore);
                     if (!mDragFromTextInput) {
                         nativeHideCursor();

core/java/android/widget/ScrollView.java

@@ -51,8 +51,6 @@ import java.util.List;
  * <p>ScrollView only supports vertical scrolling.
  */
 public class ScrollView extends FrameLayout {
-    static final String TAG = "ScrollView";
-    
     static final int ANIMATED_SCROLL_GAP = 250;
 
     static final float MAX_SCROLL_FACTOR = 0.5f;
@@ -401,6 +399,7 @@ public class ScrollView extends FrameLayout {
                 final int yDiff = (int) Math.abs(y - mLastMotionY);
                 if (yDiff > mTouchSlop) {
                     mIsBeingDragged = true;
+                    mLastMotionY = y;
                 }
                 break;