Support scrolling layers with the mousewheel

 Bug: 6635437
 Fix onGenericAction to support scrolling layers.
 Calling startScrollingLayer detects if there is a layer under
 the mouse pointer, and if so switches to DRAG_LAYER_MODE. Then, calling
 doDrag will correctly handle scrolling the layer in DRAG_LAYER_MODE,
 switching out of DRAG_LAYER_MODE when we hit the end of a layer, and
 scrolling the page if there isn't a layer. It is the method used
 by the touch drag path.

Change-Id: I00be09a63c40caa8fce94134c57db0894a62fef0

Author: jreck

core/java/android/webkit/WebViewClassic.java

@@ -6441,9 +6441,13 @@ public boolean onGenericMotionEvent(MotionEvent event) {
                                 mWebViewPrivate.getVerticalScrollFactor());
                         final int hdelta = (int) (hscroll *
                                 mWebViewPrivate.getHorizontalScrollFactor());
-                        if (pinScrollBy(hdelta, vdelta, false, 0)) {
-                            return true;
-                        }
+
+                        abortAnimation();
+                        int oldTouchMode = mTouchMode;
+                        startScrollingLayer(event.getX(), event.getY());
+                        doDrag(hdelta, vdelta);
+                        mTouchMode = oldTouchMode;
+                        return true;
                     }
                 }
             }