PPAPI: Add dev synchronous JS->Plugin messaging API

ppapi/api/ppp_message_handler.idl

Index: ppapi/api/ppp_message_handler.idl
diff --git a/ppapi/api/ppp_message_handler.idl b/ppapi/api/ppp_message_handler.idl
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+/* Copyright 2014 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.
+ */
+
+/**
+ * This file defines the <code>PPP_MessageHandler</code> interface that plugins
+ * can implement and register using PPB_Messaging::RegisterMessageHandler in
+ * order to handle messages sent from JavaScript via postMessage() or
+ * postMessageAndAwaitResponse().
+ */
+
+label Chrome {
+  [channel=none] M37 = 0.1
+};
+
+/**
+ * The <code>PPP_MessageHandler</code> interface is implemented by the plugin
+ * if the plugin wants to receive messages from a thread other than the main
+ * Pepper thread, or if the plugin wants to handle blocking messages which
+ * JavaScript may send via postMessageAndAwaitResponse().
+ *
+ * This interface struct should not be returned by PPP_GetInterface; instead it
+ * must be passed as a parameter to PPB_Messaging::RegisterMessageHandler.
+ */
+[no_interface_string]
+interface PPP_MessageHandler {
+  /**
+   * Invoked as a result of JavaScript invoking postMessage() on the plugin's
+   * DOM element.
+   *
+   * @param[in] instance A <code>PP_Instance</code> identifying one instance
+   * of a module.
+   * @param[in] user_data is the same pointer which was provided by a call to
+   * RegisterMessageHandler.
+   * @param[in] message A copy of the parameter that JavaScript provided to
+   * postMessage().
+   */
+  void HandleMessage([in] PP_Instance instance,
+                     [in] mem_t user_data,
+                     [in] PP_Var message);
+  /**
+   * Invoked as a result of JavaScript invoking postMessageAndAwaitResponse()
+   * on the plugin's DOM element.
+   *
+   * @param[in] instance A <code>PP_Instance</code> identifying one instance
+   * of a module.
+   * @param[in] user_data is the same pointer which was provided by a call to
+   * RegisterMessageHandler.
+   * @param[in] message is a copy of the parameter that JavaScript provided
+   * to postMessageAndAwaitResponse.
+   * @return will be copied to a JavaScript object which is returned as
+   * the result of postMessageAndAwaitResponse to the invoking JavaScript.
+   */
+  PP_Var HandleBlockingMessage([in] PP_Instance instance,
+                               [inout] mem_t user_data,
+                               [in] PP_Var message);
+  /**
+   * Invoked when the handler object is no longer needed. After this, no more
+   * calls will be made which pass this same value for <code>instance</code>
+   * and <code>user_data</code>.
+   *
+   * @param[in] instance A <code>PP_Instance</code> identifying one instance
+   * of a module.
+   * @param[in] user_data is the same pointer which was provided by a call to
+   * RegisterMessageHandler.
+   */
+  void Destroy([in] PP_Instance instance, [inout] mem_t user_data);
+};
+