cc: Implement shared worker contexts. (v1)

cc/test/test_context_provider.h

Index: cc/test/test_context_provider.h
diff --git a/cc/test/test_context_provider.h b/cc/test/test_context_provider.h
index 82b3e612d681344d71d0dbf603f51dcfc8f437a7..8f128f1f7488eec54cbb14f8f6977051c9006273 100644
--- a/cc/test/test_context_provider.h
+++ b/cc/test/test_context_provider.h
@@ -25,6 +25,10 @@ class TestContextProvider : public ContextProvider {
     CreateCallback;
 
   static scoped_refptr<TestContextProvider> Create();
+  // Creates a worker context provider that doesn't need to be bound to a

[danakj, 2015/08/27 18:24:01]

Hm.. but this doesn't match the real context. Diverging behaviour between the
test thing and the real thing reduces our test coverage. Can we avoid that?

[reveman, 2015/08/27 18:58:52]

Create(); BindToCurrentThread(); SetupLock(); DetachFromThread() match what we
do for real contexts. This is just an utility function to avoid doing that in a
bunch of places for tests. I can of course make the implementation of this
function explicitly do all that but with this being part of the
TestContextProvider impl I figured that was unnecessary as the end result is the
same.

[danakj, 2015/08/27 20:16:40]

The thing is we're calling this all the places that take a worker context, so
all our unit tests - including the ones that test that we do call stuff like
BindToCurrentThread - are getting a context with a different state than what a
real one would have.

I'd prefer if some set of tests would benefit from this type of thing we make it
a helper method in those tests' base class or something, I think. Is there many
tests this helps?

[reveman, 2015/08/27 20:33:07]

I'm not sure I follow. This is needed in all cases where I call it in this
patch. cc::OutputSurface will no longer call BindToCurrentThread() on the worker
context and the worker context passed to the output surface will instead have to
be bound and setup in advance. CreateWorker() does this setup so we don't have
to do it in each case where we need a worker context for tests. I don't mind
moving this helper code somewhere else. e.g. static helper function as part of
FakeOutputSurface. Just let me know what you prefer and I'll move it.

[danakj, 2015/08/27 21:06:40]

Oh.. ok I think I see what you're saying.

These methods are done by the embedder not by cc. So this is acting like how the
embedder would behave.

It's confusing that both the embedder and cc do BindToCurrentThread on the
output surface, sorry.

I think this LGTM. Thanks for talking through it.

+  // thread and can be used on any thread. This is equivalent to:
+  // Create(); BindToCurrentThread(); SetupLock(); DetachFromThread().
+  static scoped_refptr<TestContextProvider> CreateWorker();
   static scoped_refptr<TestContextProvider> Create(
       scoped_ptr<TestWebGraphicsContext3D> context);