Add a WebSettings to control whether WebView will

use some perf trick, e.g. pause updating the picture,
during panning and zooming transition.

Fix http://b/issue?id=2784020

api/current.xml

@@ -200811,6 +200811,17 @@
  deprecated="not deprecated"
  visibility="public"
 >
+<method name="enableSmoothTransition"
+ return="boolean"
+ abstract="false"
+ native="false"
+ synchronized="false"
+ static="false"
+ final="false"
+ deprecated="not deprecated"
+ visibility="public"
+>
+</method>
 <method name="getAllowFileAccess"
  return="boolean"
  abstract="false"
@@ -201426,6 +201437,19 @@
 <parameter name="flag" type="boolean">
 </parameter>
 </method>
+<method name="setEnableSmoothTransition"
+ return="void"
+ abstract="false"
+ native="false"
+ synchronized="false"
+ static="false"
+ final="false"
+ deprecated="not deprecated"
+ visibility="public"
+>
+<parameter name="enable" type="boolean">
+</parameter>
+</method>
 <method name="setFantasyFontFamily"
  return="void"
  abstract="false"

core/java/android/webkit/WebSettings.java

@@ -207,6 +207,7 @@ public class WebSettings {
     private boolean         mBuiltInZoomControls = false;
     private boolean         mAllowFileAccess = true;
     private boolean         mLoadWithOverviewMode = false;
+    private boolean         mEnableSmoothTransition = false;
 
     // private WebSettings, not accessible by the host activity
     static private int      mDoubleTapToastCount = 3;
@@ -522,6 +523,25 @@ public class WebSettings {
         return mLoadWithOverviewMode;
     }
 
+    /**
+     * Set whether the WebView will enable smooth transition while panning or
+     * zooming. If it is true, WebView will choose a solution to maximize the
+     * performance. e.g. the WebView's content may not be updated during the
+     * transition. If it is false, WebView will keep its fidelity. The default
+     * value is false.
+     */
+    public void setEnableSmoothTransition(boolean enable) {
+        mEnableSmoothTransition = enable;
+    }
+
+    /**
+     * Returns true if the WebView enables smooth transition while panning or
+     * zooming.
+     */
+    public boolean enableSmoothTransition() {
+        return mEnableSmoothTransition;
+    }
+
     /**
      * Store whether the WebView is saving form data.
      */

core/java/android/webkit/WebViewCore.java

@@ -1871,6 +1871,8 @@ final class WebViewCore {
         // called from UI thread while WEBKIT_DRAW is just pulled out of the
         // queue in WebCore thread to be executed. Then update won't be blocked.
         if (core != null) {
+            if (!core.getSettings().enableSmoothTransition()) return;
+
             synchronized (core) {
                 core.mDrawIsPaused = true;
                 if (core.mDrawIsScheduled) {
@@ -1883,6 +1885,10 @@ final class WebViewCore {
 
     static void resumeUpdatePicture(WebViewCore core) {
         if (core != null) {
+            // if mDrawIsPaused is true, ignore the setting, continue to resume
+            if (!core.mDrawIsPaused
+                    && !core.getSettings().enableSmoothTransition()) return;
+
             synchronized (core) {
                 core.mDrawIsPaused = false;
                 if (core.mDrawIsScheduled) {