Cache DeviceDisplayInfo data in shared structure on native side to avoid frequent JNI calls.

ui/android/java/src/org/chromium/ui/gfx/DeviceDisplayInfo.java

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 package org.chromium.ui.gfx;
 
 import android.content.Context;
+import android.content.ComponentCallbacks;
+import android.content.res.Configuration;
 import android.graphics.PixelFormat;
 import android.os.Build;
 import android.util.DisplayMetrics;
 import android.view.Display;
 import android.view.WindowManager;
 
 import org.chromium.base.CalledByNative;
 import org.chromium.base.JNINamespace;
 
 /**
@@ skipping 90 matching lines @@
 
   /**
    * @return A scaling factor for the Density Independent Pixel unit.
    *         1.0 is 160dpi, 0.75 is 120dpi, 2.0 is 320dpi.
    */
   @CalledByNative
   public double getDIPScale() {
       return getMetrics().density;
   }
 
+  public void registerListener() {

[Yaron, 2013/10/11 10:18:14]

private

+      mAppContext.registerComponentCallbacks(
+          new ComponentCallbacks() {
+              @Override
+              public void onConfigurationChanged(Configuration configuration) {
+                updateNativeSharedDisplayInfo();

[Yaron, 2013/10/11 10:18:14]

indent 4 for block-level (other places below too). Please also correct the C++
code

+              }
+
+              @Override
+              public void onLowMemory() {
+              }
+      });
+  }
+
+  private void updateNativeSharedDisplayInfo() {
+    nativeUpdateSharedDeviceDisplayInfo(getDisplayHeight(), getDisplayWidth(),
+      getBitsPerPixel(), getBitsPerComponent(), getDIPScale());
+  }
+
   private Display getDisplay() {
       return mWinManager.getDefaultDisplay();
   }
 
   private DisplayMetrics getMetrics() {
       return mAppContext.getResources().getDisplayMetrics();
   }
 
   /**
    * Creates DeviceDisplayInfo for a given Context.
    * @param context A context to use.
    * @return DeviceDisplayInfo associated with a given Context.
    */
-  @CalledByNative
   public static DeviceDisplayInfo create(Context context) {
       return new DeviceDisplayInfo(context);
   }
+
+  @CalledByNative
+  public static DeviceDisplayInfo createWithListener(Context context) {

[Yaron, 2013/10/11 10:18:14]

Make private. This is unneeded from the java layer

+      DeviceDisplayInfo deviceDisplayInfo = new DeviceDisplayInfo(context);
+      deviceDisplayInfo.registerListener();
+      return deviceDisplayInfo;
+  }
+
+  private native void nativeUpdateSharedDeviceDisplayInfo(int displayHeight,
+                        int displayWidth, int bitsPerPixel,
+                        int bitsPerComponent, double dipScale);
+
 }