Re-land: cc: Implement shared worker contexts.

cc/output/output_surface.cc

Index: cc/output/output_surface.cc
diff --git a/cc/output/output_surface.cc b/cc/output/output_surface.cc
index 056879f49d84ba444142101690da109437208d14..6ba290c14a9d020b3e5c748583f305ee3eb6fe52 100644
--- a/cc/output/output_surface.cc
+++ b/cc/output/output_surface.cc
@@ -32,6 +32,7 @@ OutputSurface::OutputSurface(
       device_scale_factor_(-1),
       external_stencil_test_enabled_(false),
       weak_ptr_factory_(this) {
+  client_thread_checker_.DetachFromThread();
 }
 
 OutputSurface::OutputSurface(
@@ -101,12 +102,8 @@ void OutputSurface::SetExternalDrawConstraints(
 }
 
 OutputSurface::~OutputSurface() {
-  if (context_provider_.get()) {
-    context_provider_->SetLostContextCallback(
-        ContextProvider::LostContextCallback());
-    context_provider_->SetMemoryPolicyChangedCallback(
-        ContextProvider::MemoryPolicyChangedCallback());
-  }
+  if (client_)
+    DetachFromClient();
 }
 
 bool OutputSurface::HasExternalStencilTest() const {
@@ -115,6 +112,8 @@ bool OutputSurface::HasExternalStencilTest() const {
 
 bool OutputSurface::BindToClient(OutputSurfaceClient* client) {
   DCHECK(client);
+  DCHECK(!client_);
+  DCHECK(CalledOnValidClientThread());
   client_ = client;
   bool success = true;
 
@@ -128,18 +127,30 @@ bool OutputSurface::BindToClient(OutputSurfaceClient* client) {
     }
   }
 
-  if (success && worker_context_provider_.get()) {
-    success = worker_context_provider_->BindToCurrentThread();
-    if (success)
-      worker_context_provider_->SetupLock();
-  }
-
   if (!success)
     client_ = NULL;
 
   return success;
 }
 
+void OutputSurface::DetachFromClient() {
+  DCHECK(CalledOnValidClientThread());
+  DCHECK(client_);
+  if (context_provider_.get()) {
+    context_provider_->SetLostContextCallback(
+        ContextProvider::LostContextCallback());
+    context_provider_->SetMemoryPolicyChangedCallback(
+        ContextProvider::MemoryPolicyChangedCallback());
+  }
+  context_provider_ = nullptr;
+  client_ = nullptr;
+  weak_ptr_factory_.InvalidateWeakPtrs();
+}
+
+bool OutputSurface::CalledOnValidClientThread() {
+  return client_thread_checker_.CalledOnValidThread();
+}
+
 void OutputSurface::EnsureBackbuffer() {
   if (software_device_)
     software_device_->EnsureBackbuffer();