[android_webview] Add a generic callback JNI bridge.

android_webview/native/callback_jni_bridge.h

Index: android_webview/native/callback_jni_bridge.h
diff --git a/android_webview/native/callback_jni_bridge.h b/android_webview/native/callback_jni_bridge.h
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+// Copyright 2013 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 ANDROID_WEBVIEW_NATIVE_JAVA_CALLBACK_BRIDGE_H_
+#define ANDROID_WEBVIEW_NATIVE_JAVA_CALLBACK_BRIDGE_H_
+
+#include "base/callback.h"
+#include "base/android/jni_android.h"
+#include "base/android/scoped_java_ref.h"
+
+namespace android_webview {
+
+class CallbackJNIBridge {
+ public:
+  // Creates a base::Callback the Run() method of which will delegate to the
+  // onReceiveValue method of the Java-side |value_callback| object.
+  //
+  // The returned callback will hold a global reference to the Java object, so
+  // this method should be used with short-lived callbacks only.
+  static base::Callback<void(int)> FromJavaValueCallbackInt(
+      JNIEnv* env,
+      base::android::ScopedJavaLocalRef<jobject> value_callback);
+
+  // Creates a Java object (an instance that implements the ValueCallback<Int>
+  // interface) the onReceiveValue method of which will delegate to the
+  // supplied |callback|.
+  // The callback's lifespan is tied to the Java object.
+  static base::android::ScopedJavaLocalRef<jobject> ToJavaValueCallbackInt(
+      JNIEnv* env,
+      const base::Callback<void(int)>& callback);
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(CallbackJNIBridge);
+};
+
+bool RegisterCallbackJNIBridge(JNIEnv* env);
+
+} // namespace android_webview
+
+#endif  // ANDROID_WEBVIEW_NATIVE_JAVA_CALLBACK_BRIDGE_H_