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 11 matching lines @@
   private final WindowManager mWinManager;
 
   private DeviceDisplayInfo(Context context) {
       mAppContext = context.getApplicationContext();
       mWinManager = (WindowManager) mAppContext.getSystemService(Context.WINDOW_SERVICE);
   }
 
   /**
    * @return Display height in physical pixels.
    */
-  @CalledByNative
   public int getDisplayHeight() {
       return getMetrics().heightPixels;
   }
 
   /**
    * @return Display width in physical pixels.
    */
-  @CalledByNative
   public int getDisplayWidth() {
       return getMetrics().widthPixels;
   }
 
   @SuppressWarnings("deprecation")
   private int getPixelFormat() {
       if (Build.VERSION.SDK_INT < Build.VERSION_CODES.JELLY_BEAN_MR1) {
           return getDisplay().getPixelFormat();
       }
       // JellyBean MR1 and later always uses RGBA_8888.
       return PixelFormat.RGBA_8888;
   }
 
   /**
    * @return Bits per pixel.
    */
-  @CalledByNative
   public int getBitsPerPixel() {
       int format = getPixelFormat();
       PixelFormat info = new PixelFormat();
       PixelFormat.getPixelFormatInfo(format, info);
       return info.bitsPerPixel;
   }
 
   /**
    * @return Bits per component.
    */
   @SuppressWarnings("deprecation")
-  @CalledByNative
   public int getBitsPerComponent() {
       int format = getPixelFormat();
       switch (format) {
       case PixelFormat.RGBA_4444:
           return 4;
 
       case PixelFormat.RGBA_5551:
           return 5;
 
       case PixelFormat.RGBA_8888:
@@ skipping 16 matching lines @@
       // Unknown format. Use 8 as a sensible default.
       default:
           return 8;
       }
   }
 
   /**
    * @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;
   }
 
+  @CalledByNative
+  public void registerListener() {
+    mAppContext.registerComponentCallbacks(

[Yaron, 2013/10/10 11:52:46]

nit: indent 4 (also below)

+        new ComponentCallbacks() {
+          @Override
+          public void onConfigurationChanged(Configuration configuration) {
+            updateNativeSharedDisplayInfo();
+          }

[Yaron, 2013/10/10 11:52:46]

nit: add linebreak below

+          @Override
+          public void onLowMemory() {
+          }
+        });
+
+    updateNativeSharedDisplayInfo();
+  }
+
+  private void updateNativeSharedDisplayInfo() {
+     nativeUpdateSharedDisplayInfo(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);
   }
+
+  private native void nativeUpdateSharedDisplayInfo(int display_height,

[Yaron, 2013/10/10 11:52:46]

java style should be displayHeight. Please update this and other variables

+                        int display_width, int bits_per_pixel,
+                        int bits_per_component, double dip_scale);
+
 }