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..db71bcd1109d7ab7323463eeee05c82d7c3c2eb1 100644
--- a/gpu/command_buffer/client/gles2_implementation.cc
+++ b/gpu/command_buffer/client/gles2_implementation.cc
@@ -19,6 +19,7 @@
 #include <string>
 #include "base/atomic_sequence_num.h"
 #include "base/compiler_specific.h"
+#include "base/memory/ptr_util.h"
 #include "base/strings/string_split.h"
 #include "base/strings/stringprintf.h"
 #include "base/sys_info.h"
@@ -51,6 +52,22 @@ namespace gles2 {
 
 namespace {
 
+class ScopedVisibilityImpl : public ContextSupport::ScopedVisibility {
+ public:
+  explicit ScopedVisibilityImpl(ContextSupport* context_support)
+      : initial_context_support_(context_support) {}
+  ~ScopedVisibilityImpl() { DCHECK(!initial_context_support_); }
+
+  void Release(ContextSupport* context_support) {
+    DCHECK_EQ(initial_context_support_, context_support);
+    initial_context_support_ = nullptr;
+  }
+
+ private:
+  // |initial_context_support_| is just stored/used for sanity-checking Release.

[danakj, 2016/08/19 18:29:55]

Update comment

[ericrk, 2016/08/19 18:49:58]

Done.

+  const ContextSupport* initial_context_support_;
+};
+
 void CopyRectToBuffer(const void* pixels,
                       uint32_t height,
                       uint32_t unpadded_row_size,
@@ -164,7 +181,6 @@ GLES2Implementation::GLES2Implementation(
       current_trace_stack_(0),
       gpu_control_(gpu_control),
       capabilities_(gpu_control->GetCapabilities()),
-      aggressively_free_resources_(false),
       cached_extension_string_(nullptr),
       weak_ptr_factory_(this) {
   DCHECK(helper);
@@ -5861,18 +5877,21 @@ 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() {
+  ++num_visible_clients_;
+  return base::MakeUnique<ScopedVisibilityImpl>(this);
+}
+
+void GLES2Implementation::ClientBecameNotVisible(
+    std::unique_ptr<ScopedVisibility> visibility) {
+  DCHECK_GT(num_visible_clients_, 0u);

[danakj, 2016/08/19 18:29:55]

can you DCHECK(visibility) too? (same for the TestContextSupport I guess also)

[ericrk, 2016/08/19 18:49:58]

Done.

+  --num_visible_clients_;
+  static_cast<ScopedVisibilityImpl*>(visibility.get())->Release(this);
 }
 
 bool GLES2Implementation::AnyClientsVisible() const {
-  return !visible_clients_.empty();
+  return num_visible_clients_ > 0;
 }
 
 void GLES2Implementation::SetLostContextCallback(