Refactor client visibility handling

cc/output/context_cache_controller.h

Index: cc/output/context_cache_controller.h
diff --git a/cc/output/context_cache_controller.h b/cc/output/context_cache_controller.h
new file mode 100644
index 0000000000000000000000000000000000000000..bcf0b3a88d2b4b98298fe45340cbb2f1cda116a7
--- /dev/null
+++ b/cc/output/context_cache_controller.h
@@ -0,0 +1,64 @@
+// Copyright (c) 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CC_OUTPUT_CONTEXT_CACHE_CONTROLLER_H_
+#define CC_OUTPUT_CONTEXT_CACHE_CONTROLLER_H_
+
+#include <cstdint>
+#include <memory>
+
+#include "base/macros.h"
+#include "cc/base/cc_export.h"
+
+class GrContext;
+
+namespace gpu {
+class ContextSupport;
+}
+
+namespace cc {
+
+// ContextCacheController manages clearing cached data on ContextProvider when

[danakj, 2016/08/26 23:49:08]

My one thought is that it's a bit weird that the impl of this is in cc, cuz you
have to dep on cc/ to use GPU things without cc things.. It's equally weird that
the context provider API is in cc tho, I guess they can both move to gpu at the
same time one day

[ericrk, 2016/08/29 22:43:22]

Yeah, I had a similar thought, but I assumed there was a reason for
ContextProvider to be there :P, if not, then yeah, this can really go anywhere
(probably GPU is best)...

+// appropriate. Currently, cache clearing happens when the Context provider

[danakj, 2016/08/26 23:49:08]

when the ContextProvider

[ericrk, 2016/08/29 22:43:22]

Done.

+// transitions from Visible to Not Visible. As a ContextProvider may have

[danakj, 2016/08/26 23:49:08]

visible to not visible

[ericrk, 2016/08/29 22:43:22]

Done.

+// multiple clients, ContextCacheController tracks visibility across all
+// clients and only cleans up when appropriate.
+class CC_EXPORT ContextCacheController {

[ericrk, 2016/08/26 22:55:47]

This name is a bit silly - I'm thinking of a better one :P

[danakj, 2016/08/26 23:49:08]

lies it's perfect

+ public:
+  class ScopedVisibility {
+   public:
+    ~ScopedVisibility();
+
+   private:
+    friend class ContextCacheController;
+    ScopedVisibility();
+    void Release();
+
+    bool released_ = false;
+  };
+
+  explicit ContextCacheController(gpu::ContextSupport* context_support);
+  void SetGrContext(GrContext* gr_context);

[danakj, 2016/08/26 23:49:08]

whitespace after constructors/destructor plz

[ericrk, 2016/08/29 22:43:22]

Done.

+
+  // Clients of the owning ContextProvider should call this function when they
+  // become visible. The returned ScopedVisibility pointer must be passed back
+  // to ClientBecameNotVisible or it will DCHECK in its destructor.
+  std::unique_ptr<ScopedVisibility> ClientBecameVisible();
+
+  // When a client becomes not visible (either due to a visibility change or
+  // because it is being deleted), it must pass back any ScopedVisibility
+  // pointers it owns via this function.
+  void ClientBecameNotVisible(
+      std::unique_ptr<ScopedVisibility> scoped_visibility);
+
+ private:
+  gpu::ContextSupport* context_support_;
+  GrContext* gr_context_ = nullptr;
+
+  uint32_t num_clients_visible_ = 0;
+};
+
+}  // namespace cc
+
+#endif  // CC_OUTPUT_CONTEXT_CACHE_CONTROLLER_H_