Add extensions code to use common updater in components/update_client/

extensions/browser/test_extensions_browser_client.cc

Index: extensions/browser/test_extensions_browser_client.cc
diff --git a/extensions/browser/test_extensions_browser_client.cc b/extensions/browser/test_extensions_browser_client.cc
index be9e4b5c30e99da966f3e29ba93d99e5f3d42be5..47eceba502ebbac851d7b336a628ef6828b60328 100644
--- a/extensions/browser/test_extensions_browser_client.cc
+++ b/extensions/browser/test_extensions_browser_client.cc
@@ -200,4 +200,10 @@ TestExtensionsBrowserClient::GetExtensionWebContentsObserver(
   return nullptr;
 }
 
+scoped_refptr<update_client::UpdateClient>
+TestExtensionsBrowserClient::CreateUpdateClient(
+    content::BrowserContext* context) {
+  return update_client_.Pass();

[Sorin Jianu, 2015/10/02 00:05:10]

How does this work? I see that update_client_ instance has a setter. Will the
code guarantee that the instance is always set and we are not trying to create
too many instances of the update client by calling this function?

[asargent_no_longer_on_chrome, 2015/10/06 21:31:17]

This is very similar to using .Pass with something like a scoped_ptr - it passes
off ownership from one thing to another. In this case, the caller gets returned
a scoped_refptr pointing to the same object that update_client_ did, and
update_client_ gets set to nullptr. 

(If you want to see the gory details of how .Pass works, it comes from the usage
of the TYPE_WITH_MOVE_CONSTRUCTOR_FOR_CPP_03 macro on the scoped_refptr class;
that macro is defined in move.h)

So nothing is getting created here - this is just test code that relies on the
fact that some other test code previously created an UpdateClient that they want
returned by the next CreateUpdateClient call. 

[Sorin Jianu, 2015/10/08 22:57:54]

Correct. I am concerned that successive calls for
TestExtensionsBrowserClient::CreateUpdateClient don't create new instances of
UpdateClient. In other words, we see here a factory function named
CreateUpdateClient. We expect this function to return a new instance of the
object every time is it called.

[asargent_no_longer_on_chrome, 2015/10/14 17:04:31]

Ok, I've rewritten this so that TestExtensionsBrowserClient now takes a callback
to register a factory callback to vend UpdateClient instances. 

[Sorin Jianu, 2015/10/14 20:37:09]

Acknowledged.

+}
+
 }  // namespace extensions