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 6ffd79dabdbee355d0383aee2861d41584e3e79d..81fc05ff4d4944cd8e3d57cd9231951a5bf44fdc 100644
--- a/blimp/engine/browser/blimp_engine_session.cc
+++ b/blimp/engine/browser/blimp_engine_session.cc
@@ -17,6 +17,7 @@
 #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"
@@ -107,7 +108,9 @@ 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()) {
@@ -122,7 +125,7 @@ net::Error BlimpEngineSession::OnBlimpMessage(const BlimpMessage& message) {
       NOTIMPLEMENTED();
   }
 
-  return net::OK;
+  callback.Run(net::OK);

[Wez, 2015/11/12 03:45:56]

Didn't we agree that ProcessMessage should be required to handle null callbacks?

[Kevin M, 2015/11/12 19:03:47]

Done.

 }
 
 void BlimpEngineSession::AddNewContents(content::WebContents* source,