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/lazy_instance.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 GFX_EXPORT SharedDeviceDisplayInfo {

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

Doesn't actually need to be exported, right? 

+ public:
+  SharedDeviceDisplayInfo();
+  static SharedDeviceDisplayInfo* Instance();

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

No need to expose this publicly. Move g_instance into an anonymous namespace in
the cc file. That way UpdateSharedDisplayInfo can access it without making it
visible.

+
+  static int GetDisplayHeight();
+  static int GetDisplayWidth();
+  static int GetBitsPerPixel();
+  static int GetBitsPerComponent();
+  static double GetDIPScale();
+
+  void UpdateDisplayInfo(JNIEnv*, jobject, jint display_height,
+        jint display_width, jint bits_per_pixel, jint bits_per_component,
+        jdouble dip_scale);
+
+  // Registers methods with JNI and returns true if succeeded.
+  static bool RegisterSharedDeviceDisplayInfo(JNIEnv* env);
+
+  base::Lock& lock() { return lock_; }

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

Prefer not to expose this either. Locking should be internal to this class.

+ private:
+  static base::LazyInstance<SharedDeviceDisplayInfo> g_instance_;
+
+  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_;
+
+  DISALLOW_COPY_AND_ASSIGN(SharedDeviceDisplayInfo);
+};
+
+}  // namespace gfx
+
+#endif // UI_GFX_ANDROID_SHARED_DEVICE_DISPLAY_INFO_H_