Enable overriding interface binders for any services running in current process.

services/service_manager/public/cpp/service_context.h

Index: services/service_manager/public/cpp/service_context.h
diff --git a/services/service_manager/public/cpp/service_context.h b/services/service_manager/public/cpp/service_context.h
index 451f1ad0c8e297a65de8f14350be03ef6f6498b0..03571874aeb16974bb389fd719f352fa09bd35f8 100644
--- a/services/service_manager/public/cpp/service_context.h
+++ b/services/service_manager/public/cpp/service_context.h
@@ -42,6 +42,32 @@ namespace service_manager {
 // client.
 class ServiceContext : public mojom::Service {
  public:
+  class TestApi {

[Ken Rockot(use gerrit already), 2017/05/09 15:29:34]

nit: I'm not really a fan of these TestApi subclasses. I'd rather we just
introduce a minimal set of testing methods directly on ServiceContext, e.g.:

  ServiceContext::SetGlobalBinderForTesting()
  ServiceContext::ClearGlobalBindersForTesting()

[leonhsl(Using Gerrit), 2017/05/09 23:31:53]

Acknowledged.

[leonhsl(Using Gerrit), 2017/05/10 09:57:11]

Done.

+   public:
+    ~TestApi() = default;
+
+    // Overrides the interface binder for |interface_name| of |service|. This is
+    // a process-wide override, means that |binder| can intercept requests only
+    // if |service| runs in the same process with caller of this function.
+    // You can specify |service| as identity of a particular instance of service
+    // "Foo", or just an identity only having the name "Foo" to specify any
+    // instances of service "Foo" in general.
+    static void SetGlobalBinder(
+        const Identity& service,

[Ken Rockot(use gerrit already), 2017/05/09 15:29:34]

I wonder if we really want a specific identity to override against, or if we
want to override all requests for |interface_name| to all instances of
(service.name()), in which case we should take a std::string (name) instead of a
full Identity. I suspect that's what we want.

[leonhsl(Using Gerrit), 2017/05/09 23:31:53]

Yeah I was afraid in future some test cases may want to override against a
specific instance of service, though I have no clear image about such test
cases:) so I chose to make this API more flexible considering that it will be a
public API from service manager client library. User can still override for all
instances of service "Foo" with an Identity("Foo"). 
Or we're sure that definitely there have no such needs?

[blundell, 2017/05/10 08:54:39]

Let's leave it simple for now and it will be easy enough to introduce the
flexibility later if needed. 

[leonhsl(Using Gerrit), 2017/05/10 09:57:11]

I see, will update CL soon.

[leonhsl(Using Gerrit), 2017/05/11 02:21:47]

Done.

+        const std::string& interface_name,
+        const base::Callback<void(mojo::ScopedMessagePipeHandle)>& binder,

[Ken Rockot(use gerrit already), 2017/05/09 15:29:34]

In keeping with existing binder callbacks today, this should be a

base::Callback<void(const service_manager::BindSourceInfo& source_info,
                    const std::string& interface_name,
                    mojo::ScopedMessagePipeHandle pipe)>;

In fact you could update the (currently unused) BinderRegistry::Binder alias to
that signature and use it here (and possibly elsewhere).

Even if most uses of the test API will ignore source_info and interface_name,
this it a bit more flexibility.

[leonhsl(Using Gerrit), 2017/05/09 23:31:53]

Acknowledged.

[leonhsl(Using Gerrit), 2017/05/10 09:57:11]

Done and Thanks!

+        const scoped_refptr<base::SingleThreadTaskRunner>& task_runner =
+            nullptr);
+
+    // Clears all overridden interface binders for |service|.
+    static void ClearGlobalBinders(const Identity& service);

[blundell, 2017/05/05 12:56:07]

nit: Maybe ClearGlobalBindersForService()?

[leonhsl(Using Gerrit), 2017/05/09 00:08:54]

Acknowledged.

+
+   private:
+    TestApi() = default;
+
+    DISALLOW_COPY_AND_ASSIGN(TestApi);
+  };
+
   // Creates a new ServiceContext bound to |request|. This connection may be
   // used immediately to make outgoing connections via connector().
   //