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..1098a4030e0e60e9941e2b3b40fc4a984c717030 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 that DCHECKs if it is destructed without first having Release called.
+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:
+  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);
@@ -412,11 +428,12 @@ void GLES2Implementation::SignalQuery(uint32_t query,
                  callback));
 }
 
-void GLES2Implementation::SetAggressivelyFreeResources(
-    bool aggressively_free_resources) {
-  TRACE_EVENT1("gpu", "GLES2Implementation::SetAggressivelyFreeResources",
-               "aggressively_free_resources", aggressively_free_resources);
-  aggressively_free_resources_ = aggressively_free_resources;
+void GLES2Implementation::TrimResources() {
+  TRACE_EVENT0("gpu", "GLES2Implementation::TrimResources");
+
+  // Set aggressively_free_resources_ to true, which will cause us to free
+  // resources when we call Flush or ShallowFlushCHROMIUM below.
+  aggressively_free_resources_ = true;
 
   if (aggressively_free_resources_ && helper_->HaveRingBuffer()) {
     // Ensure that we clean up as much cache memory as possible and fully flush.
@@ -428,6 +445,10 @@ void GLES2Implementation::SetAggressivelyFreeResources(
   } else {
     ShallowFlushCHROMIUM();
   }
+
+  // If we are not visible, continue freeing resources on subsequent flushes.
+  // This will be set to false once we become visible.
+  aggressively_free_resources_ = !AnyClientsVisible();
 }
 
 bool GLES2Implementation::OnMemoryDump(
@@ -5861,18 +5882,24 @@ 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_;
+  // We are visible, ensure that we are no longer freeing resources on flush.
+  aggressively_free_resources_ = false;
+  return base::MakeUnique<ScopedVisibilityImpl>(this);
+}
+
+void GLES2Implementation::ClientBecameNotVisible(
+    std::unique_ptr<ScopedVisibility> visibility) {
+  DCHECK(visibility);
+  DCHECK_GT(num_visible_clients_, 0u);
+  --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(