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"
+
+namespace gfx {
+
+// Facilitates access to device information typically only
+// available using the Android SDK, including Display properties.
+class SharedDeviceDisplayInfo {
+ public:
+  static SharedDeviceDisplayInfo* GetInstance();
+
+  int GetDisplayHeight();
+  int GetDisplayWidth();
+  int GetBitsPerPixel();
+  int GetBitsPerComponent();
+  double GetDIPScale();
+  int GetSmallestDIPWidth();
+
+  // Registers methods with JNI and returns true if succeeded.
+  static bool RegisterSharedDeviceDisplayInfo(JNIEnv* env);
+
+  void InvokeUpdate(JNIEnv* env,
+                    jobject jobj,
+                    jint display_height,
+                    jint display_width,
+                    jint bits_per_pixel,
+                    jint bits_per_component,
+                    jdouble dip_scale,
+                    jint smallest_dip_width);
+ private:
+  friend struct DefaultSingletonTraits<SharedDeviceDisplayInfo>;
+
+  SharedDeviceDisplayInfo();
+  ~SharedDeviceDisplayInfo();
+  void UpdateDisplayInfo(JNIEnv* env,
+                         jobject jobj,
+                         jint display_height,
+                         jint display_width,
+                         jint bits_per_pixel,
+                         jint bits_per_component,
+                         jdouble dip_scale,
+                         jint smallest_dip_width);
+
+  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_;
+  int smallest_dip_width_;
+
+  DISALLOW_COPY_AND_ASSIGN(SharedDeviceDisplayInfo);
+};
+
+}  // namespace gfx
+
+#endif // UI_GFX_ANDROID_SHARED_DEVICE_DISPLAY_INFO_H_