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

ui/gfx/android/shared_device_display_info.h

+// 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.
+
+#ifndef UI_GFX_ANDROID_SHARED_DEVICE_DISPLAY_INFO_H_
+#define UI_GFX_ANDROID_SHARED_DEVICE_DISPLAY_INFO_H_
+
+#include "base/android/scoped_java_ref.h"
+#include "base/basictypes.h"
+#include "base/memory/singleton.h"
+#include "base/synchronization/lock.h"
+#include "ui/gfx/gfx_export.h"
+
+namespace gfx {
+
+// Facilitates access to device information typically only
+// available using the Android SDK, including Display properties.
+class SharedDeviceDisplayInfo {
+ public:
+  static int GetDisplayHeight();
+  static int GetDisplayWidth();
+  static int GetBitsPerPixel();
+  static int GetBitsPerComponent();
+  static double GetDIPScale();
+
+  // Registers methods with JNI and returns true if succeeded.
+  static bool RegisterSharedDeviceDisplayInfo(JNIEnv* env);
+
+  static void InvokeUpdate(JNIEnv* env,
+                           jobject jobj,
+                           jint display_height,
+                           jint display_width,
+                           jint bits_per_pixel,
+                           jint bits_per_component,
+                           jdouble dip_scale);
+ private:
+  SharedDeviceDisplayInfo();
+  void UpdateDisplayInfo(JNIEnv* env,
+                         jobject jobj,
+                         jint display_height,
+                         jint display_width,
+                         jint bits_per_pixel,
+                         jint bits_per_component,
+                         jdouble dip_scale);
+
+  base::Lock& lock() { return lock_; }
+  static SharedDeviceDisplayInfo* GetInstance();
+
+  base::Lock lock_;
+  base::android::ScopedJavaGlobalRef<jobject> j_device_info_;
+
+  int display_height_;
+  int display_width_;
+  int bits_per_pixel_;
+  int bits_per_component_;
+  double dip_scale_;
+
+  friend class DefaultSingletonTraits<SharedDeviceDisplayInfo>;

[Alexei Svitkine (slow), 2013/10/15 15:13:07]

This should go right after the private: line.

+  friend class Singleton<SharedDeviceDisplayInfo>;

[Alexei Svitkine (slow), 2013/10/15 15:13:07]

Is this needed? I don't see other singletons using it (e.g.
https://code.google.com/p/chromium/codesearch#chromium/src/base/android/activ...
)

[ostap, 2013/10/15 18:41:24]

Yes it is needed because it Singleton refers to GetInstance() and it is private.
ActivityStatus has GetInstance() public.

+  DISALLOW_COPY_AND_ASSIGN(SharedDeviceDisplayInfo);
+};
+
+}  // namespace gfx
+
+#endif // UI_GFX_ANDROID_SHARED_DEVICE_DISPLAY_INFO_H_