Add an api to set WebView over scroll background.

If the WebView doesn't support zoom, or WebView does
not use wide viewport and horizontal is just fit,
don't do over scroll.

Fix http://b/issue?id=2498403
Fix http://b/issue?id=2497901

api/current.xml

@@ -193450,6 +193450,17 @@
  visibility="public"
 >
 </method>
+<method name="getUseSystemOverscrollBackground"
+ return="boolean"
+ abstract="false"
+ native="false"
+ synchronized="false"
+ static="false"
+ final="false"
+ deprecated="not deprecated"
+ visibility="public"
+>
+</method>
 <method name="getUseWideViewPort"
  return="boolean"
  abstract="false"
@@ -194029,6 +194040,19 @@
 <parameter name="use" type="boolean">
 </parameter>
 </method>
+<method name="setUseSystemOverscrollBackground"
+ return="void"
+ abstract="false"
+ native="false"
+ synchronized="false"
+ static="false"
+ final="false"
+ deprecated="not deprecated"
+ visibility="public"
+>
+<parameter name="system" type="boolean">
+</parameter>
+</method>
 <method name="setUseWideViewPort"
  return="void"
  abstract="false"

core/java/android/webkit/WebSettings.java

@@ -192,6 +192,7 @@ public class WebSettings {
     private boolean         mBuiltInZoomControls = false;
     private boolean         mAllowFileAccess = true;
     private boolean         mLoadWithOverviewMode = false;
+    private boolean         mUseSystemOverscrollBackground = false;
 
     // private WebSettings, not accessible by the host activity
     static private int      mDoubleTapToastCount = 3;
@@ -469,6 +470,23 @@ public class WebSettings {
         return mLoadWithOverviewMode;
     }
 
+    /**
+     * Set whether the WebView uses system background for over scroll
+     * background. If false, it will use the WebView's background. Default is
+     * false.
+     */
+    public void setUseSystemOverscrollBackground(boolean system) {
+        mUseSystemOverscrollBackground = system;
+    }
+
+    /**
+     * Returns true if this WebView uses system background instead of WebView
+     * background for over scroll background.
+     */
+    public boolean getUseSystemOverscrollBackground() {
+        return mUseSystemOverscrollBackground;
+    }
+
     /**
      * Store whether the WebView is saving form data.
      */

core/java/android/webkit/WebView.java

@@ -2305,9 +2305,11 @@ public class WebView extends AbsoluteLayout
             boolean clampedY) {
         mInOverScrollMode = false;
         int maxX = computeMaxScrollX();
-        if (Math.abs(mMinZoomScale - mMaxZoomScale) < 0.01f && maxX == 0) {
-            // do not over scroll x if the page can't be zoomed and it just fits
-            // the screen
+        if (maxX == 0 && (Math.abs(mMinZoomScale - mMaxZoomScale) < 0.01f)
+                || !getSettings().supportZoom()
+                || !getSettings().getUseWideViewPort()) {
+            // do not over scroll x if the page just fits the screen and it
+            // can't zoom or the view doesn't use wide viewport
             scrollX = pinLocX(scrollX);
         } else if (scrollX < 0 || scrollX > maxX) {
             mInOverScrollMode = true;
@@ -3112,7 +3114,8 @@ public class WebView extends AbsoluteLayout
         }
 
         int saveCount = canvas.save();
-        if (mInOverScrollMode) {
+        if (mInOverScrollMode
+                && getSettings().getUseSystemOverscrollBackground()) {
             if (mOverScrollBackground == null) {
                 mOverScrollBackground = new Paint();
                 Bitmap bm = BitmapFactory.decodeResource(