Add interfaces for most major Blimp net components.

blimp/engine/browser/blimp_engine_session.cc

Index: blimp/engine/browser/blimp_engine_session.cc
diff --git a/blimp/engine/browser/blimp_engine_session.cc b/blimp/engine/browser/blimp_engine_session.cc
index e4744d9c8d5a3d6631f56c120e531bbbdbb2d89f..e65781910e1b8003c066a22dbcf644de446179bd 100644
--- a/blimp/engine/browser/blimp_engine_session.cc
+++ b/blimp/engine/browser/blimp_engine_session.cc
@@ -4,6 +4,7 @@
 
 #include "blimp/engine/browser/blimp_engine_session.h"
 
+#include "base/bind_helpers.h"
 #include "blimp/common/proto/blimp_message.pb.h"
 #include "blimp/common/proto/control.pb.h"
 #include "blimp/engine/browser/blimp_browser_context.h"
@@ -17,6 +18,7 @@
 #include "content/public/browser/render_view_host.h"
 #include "content/public/browser/render_widget_host.h"
 #include "content/public/browser/web_contents.h"
+#include "net/base/net_errors.h"
 #include "ui/aura/client/default_capture_client.h"
 #include "ui/aura/env.h"
 #include "ui/aura/window.h"
@@ -96,11 +98,11 @@ void BlimpEngineSession::AttachClientConnection(
   BlimpMessage message;
   message.set_type(BlimpMessage::CONTROL);
   message.mutable_control()->set_type(ControlMessage::CREATE_TAB);
-  OnBlimpMessage(message);
+  ProcessMessage(message, base::Callback<void(int)>());

[haibinlu, 2015/11/04 20:33:20]

net::CompletionCallback() ?

[Kevin M, 2015/11/04 20:49:48]

Done.

   message.mutable_control()->set_type(ControlMessage::LOAD_URL);
   message.mutable_control()->mutable_load_url()->set_url(
       "https://www.google.com/");
-  OnBlimpMessage(message);
+  ProcessMessage(message, base::Callback<void(int)>());
 }
 
 void BlimpEngineSession::CreateWebContents(const int target_tab_id) {
@@ -124,7 +126,9 @@ void BlimpEngineSession::LoadUrl(const int target_tab_id, const GURL& url) {
   web_contents_->Focus();
 }
 
-net::Error BlimpEngineSession::OnBlimpMessage(const BlimpMessage& message) {
+void BlimpEngineSession::ProcessMessage(
+    const BlimpMessage& message,
+    const net::CompletionCallback& callback) {
   DCHECK(message.type() == BlimpMessage::CONTROL);
 
   switch (message.control().type()) {
@@ -138,8 +142,6 @@ net::Error BlimpEngineSession::OnBlimpMessage(const BlimpMessage& message) {
     default:
       NOTIMPLEMENTED();
   }

[haibinlu, 2015/11/04 20:33:20]

invoke callback with net::OK?

[Kevin M, 2015/11/04 20:49:48]

Done.

-
-  return net::OK;
 }
 
 void BlimpEngineSession::AddNewContents(content::WebContents* source,