Enable posting a message from JS to Android webview.

android_webview/common/aw_message_port_messages.h

Index: android_webview/common/aw_message_port_messages.h
diff --git a/android_webview/common/aw_message_port_messages.h b/android_webview/common/aw_message_port_messages.h
new file mode 100644
index 0000000000000000000000000000000000000000..74c08980872a21719a8a4cbabe4be46d37789056
--- /dev/null
+++ b/android_webview/common/aw_message_port_messages.h
@@ -0,0 +1,32 @@
+// 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.
+
+// Multiply-included file, no traditional include guard.
+#include <vector>
+
+#include "base/basictypes.h"
+#include "ipc/ipc_message_macros.h"
+
+#define IPC_MESSAGE_START AwMessagePortMsgStart
+
+//-----------------------------------------------------------------------------
+// MessagePort messages
+// These are messages sent from the browser to the renderer process.
+
+// Tells the renderer to convert the sent message from a WebSerializeScript
+// format to a base::Value. Due to the complexities of renderer/browser

[palmer, 2015/01/15 20:31:51]

Nit: The type in the response message is base::ListValue. The comment and the
code should match.

[sgurun-gerrit only, 2015/01/15 21:21:31]

Done.

+// relation, this can only be done in renderer for now.
+IPC_MESSAGE_ROUTED3(AwMessagePortMsg_Message,
+                    int /* recipient message port id */,
+                    base::string16 /* message */,

[palmer, 2015/01/15 20:31:51]

Are there any lexical, syntactic, or size constraints on |message|? Can they be
better expressed with a type — e.g. WebSerializeScript, or other?

[sgurun-gerrit only, 2015/01/15 21:21:31]

Not that I know of. There is one other place that I know the messages cross
renderer-browser boundary, and there they are converted to a base::String16
https://code.google.com/p/chromium/codesearch#chromium/src/content/common/vie...

used in:

bool RenderFrameImpl::willCheckAndDispatchMessageEvent(
    blink::WebLocalFrame* source_frame,
    blink::WebFrame* target_frame,
    blink::WebSecurityOrigin target_origin,
    blink::WebDOMMessageEvent event) {
  DCHECK(!frame_ || frame_ == target_frame);

  if (!is_swapped_out_)
    return false;

  ViewMsg_PostMessage_Params params;
  params.is_data_raw_string = false;
  params.data = event.data().toString();

...

+                    std::vector<int> /* sent message port_ids */)
+
+//-----------------------------------------------------------------------------
+// These are messages sent from the renderer to the browser process.
+
+// Response to AwMessagePortMessage_ConvertMessage
+IPC_MESSAGE_ROUTED3(AwMessagePortHostMsg_ConvertedMessage,
+                    int /* recipient message port id */,
+                    base::ListValue /* converted message */,
+                    std::vector<int> /* sent message port_ids */)