Create and integrate a metrics service client into Blimp engine.

blimp/engine/session/blimp_engine_session.cc

Index: blimp/engine/session/blimp_engine_session.cc
diff --git a/blimp/engine/session/blimp_engine_session.cc b/blimp/engine/session/blimp_engine_session.cc
index 06f1faf1c4d105fb3b0a0b55079377acebb2e769..5017d5ea112abde56d74deb4039db0913764de16 100644
--- a/blimp/engine/session/blimp_engine_session.cc
+++ b/blimp/engine/session/blimp_engine_session.cc
@@ -260,6 +260,8 @@ void BlimpEngineSession::Initialize() {
 
   RegisterFeatures();
 
+  browser_context_->Initialize();

[Wez, 2016/04/26 01:38:19]

nit: Add a one-line comment to explain what this is for?

Seems strange that this only became required when we started doing metrics...

[Jess, 2016/04/26 21:24:11]

Done.

+
   // Initialize must only be posted after the RegisterFeature calls have
   // completed.
   content::BrowserThread::PostTask(
@@ -269,6 +271,10 @@ void BlimpEngineSession::Initialize() {
                  engine_config_->client_token()));
 }
 
+void BlimpEngineSession::Finalize() {
+  browser_context_->Finalize();

[Wez, 2016/04/26 01:38:19]

Is it important that this happen before we enter the BlimpEngineSession dtor, or
could we move it there and avoid the explicit Finalize() API?

[Jess, 2016/04/26 21:24:11]

Done.

Also moved call to browser_context_->Initialize() into ctor.

+}
+
 void BlimpEngineSession::RegisterFeatures() {
   thread_pipe_manager_.reset(new ThreadPipeManager(
       content::BrowserThread::GetMessageLoopProxyForThread(