Enable posting a message from JS to Android webview.

android_webview/browser/aw_message_port_message_filter.h

Index: android_webview/browser/aw_message_port_message_filter.h
diff --git a/android_webview/browser/aw_message_port_message_filter.h b/android_webview/browser/aw_message_port_message_filter.h
new file mode 100644
index 0000000000000000000000000000000000000000..d63774bb9b216c86843b7a6c9bedd5f8e1fe77c5
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+++ b/android_webview/browser/aw_message_port_message_filter.h
@@ -0,0 +1,45 @@
+// Copyright 2015 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_BROWSER_MESSAGE_PORT_MESSAGE_FILTER_H_
+#define ANDROID_WEBVIEW_BROWSER_MESSAGE_PORT_MESSAGE_FILTER_H_
+
+#include "base/callback.h"
+#include "content/public/browser/browser_message_filter.h"
+#include "content/public/browser/message_port_delegate.h"
+
+namespace android_webview {
+
+// Filter for Aw specific MessagePort related IPC messages (creating and
+// destroying a MessagePort, sending a message via a MessagePort etc).
+class AwMessagePortMessageFilter : public content::BrowserMessageFilter,
+                                   public content::MessagePortDelegate {
+ public:
+  explicit AwMessagePortMessageFilter(int route_id);
+
+  // BrowserMessageFilter implementation.
+  void OnChannelClosing() override;
+  bool OnMessageReceived(const IPC::Message& message) override;
+  void OnDestruct() const override;
+
+  // MessagePortDelegate implementation.
+  void SendMessage(int msg_port_route_id,
+                   const base::string16& message,

[palmer, 2015/01/21 01:56:19]

I don't quite believe :) that |message| does not have *any* lexical, syntactic,
or even size constraints. What is an example of a typical value for |message|?

If it's truly an opaque blob of data, you're better off expressing that with
std::vector<uint8_t>.

[sgurun-gerrit only, 2015/01/21 02:25:54]

I think my answer was not well worded before, sorry about that. I don't mean
that there are no constraints on the format, the format is already known, it has
to be a WebSerializedScriptValue. But browser does not have logic to
deserialize/serialize a Webserializedscriptvalue.

Normally for a browser, this is a truly opaque data that browser does not
operate on it. It simply routes it to the receiver message port. 

Here browser routes this opaque data to renderer so that it can be converted to
a format it understands.

The message port logic already uses base::string16 rather then
std::vector<uint8_t> (here we simply use the existing logic). If
std::vector<uint8_t> a better choice, an owner of message port service, or maybe
even I can take a look it but I think it should be a separate CL.

+                   const std::vector<int>& sent_message_port_ids) override;
+  void SendMessagesAreQueued(int route_id) override;
+
+ private:
+  friend class content::BrowserThread;
+  friend class base::DeleteHelper<AwMessagePortMessageFilter>;
+
+  ~AwMessagePortMessageFilter() override;
+
+  int route_id_;
+
+  DISALLOW_COPY_AND_ASSIGN(AwMessagePortMessageFilter);
+};
+
+}   // namespace android_webview
+
+#endif  // ANDROID_WEBVIEW_BROWSER_MESSAGE_PORT_MESSAGE_FILTER_H_