Update Context Client Visibility to use Scoped Pattern

gpu/command_buffer/client/gles2_implementation.cc

Index: gpu/command_buffer/client/gles2_implementation.cc
diff --git a/gpu/command_buffer/client/gles2_implementation.cc b/gpu/command_buffer/client/gles2_implementation.cc
index d2f959c11b23f2ce34f6cd3c01ac053595704877..e6110941fa91f09ddaaa8984f11e883cc5d15819 100644
--- a/gpu/command_buffer/client/gles2_implementation.cc
+++ b/gpu/command_buffer/client/gles2_implementation.cc
@@ -32,6 +32,7 @@
 #include "gpu/command_buffer/client/gpu_control.h"
 #include "gpu/command_buffer/client/program_info_manager.h"
 #include "gpu/command_buffer/client/query_tracker.h"
+#include "gpu/command_buffer/client/scoped_visibility_impl.h"
 #include "gpu/command_buffer/client/shared_memory_limits.h"
 #include "gpu/command_buffer/client/transfer_buffer.h"
 #include "gpu/command_buffer/client/vertex_array_object_manager.h"
@@ -165,6 +166,7 @@ GLES2Implementation::GLES2Implementation(
       gpu_control_(gpu_control),
       capabilities_(gpu_control->GetCapabilities()),
       aggressively_free_resources_(false),
+      visible_clients_(0),
       cached_extension_string_(nullptr),
       weak_ptr_factory_(this) {
   DCHECK(helper);
@@ -5861,18 +5863,22 @@ void GLES2Implementation::SetErrorMessageCallback(
   error_message_callback_ = callback;
 }
 
-void GLES2Implementation::SetClientVisible(int client_id, bool is_visible) {
-  if (is_visible) {
-    visible_clients_.insert(client_id);
-  } else {
-    auto found = visible_clients_.find(client_id);
-    if (found != visible_clients_.end())
-      visible_clients_.erase(found);
-  }
+std::unique_ptr<ContextSupport::ScopedVisibility>
+GLES2Implementation::ClientBecameVisible() {
+  ++visible_clients_;
+  return std::unique_ptr<gpu::ScopedVisibilityImpl>(
+      new gpu::ScopedVisibilityImpl(this));
+}
+
+void GLES2Implementation::ClientBecameNotVisible(
+    std::unique_ptr<ScopedVisibility> visibility) {
+  DCHECK_GT(visible_clients_, 0u);
+  --visible_clients_;
+  static_cast<ScopedVisibilityImpl*>(visibility.get())->Release(this);

[danakj, 2016/08/18 21:39:44]

I think maybe just define this class in this .cc file unless you're going to
make it a first class part of the API.

[ericrk, 2016/08/19 17:23:19]

Done.

 }
 
 bool GLES2Implementation::AnyClientsVisible() const {
-  return !visible_clients_.empty();
+  return visible_clients_ > 0;
 }
 
 void GLES2Implementation::SetLostContextCallback(