compositor-worker: Share a thread and an isolate for compositor workers.

Source/modules/compositorworker/CompositorWorkerManager.h

Index: Source/modules/compositorworker/CompositorWorkerManager.h
diff --git a/Source/modules/compositorworker/CompositorWorkerManager.h b/Source/modules/compositorworker/CompositorWorkerManager.h
new file mode 100644
index 0000000000000000000000000000000000000000..69f1b5543edd6c1807a9123a97918ec04471e72c
--- /dev/null
+++ b/Source/modules/compositorworker/CompositorWorkerManager.h
@@ -0,0 +1,54 @@
+// Copyright 2015 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 CompositorWorkerManager_h
+#define CompositorWorkerManager_h
+
+#include "core/workers/WorkerV8Isolate.h"
+#include "modules/ModulesExport.h"
+#include "wtf/OwnPtr.h"
+#include "wtf/PassOwnPtr.h"
+#include "wtf/ThreadingPrimitives.h"
+#include <v8.h>
+
+namespace blink {
+
+class WebThreadSupportingGC;
+
+class MODULES_EXPORT CompositorWorkerManager final {
+public:
+    static void initialize();
+    static void shutdown();
+
+    static CompositorWorkerManager* instance();
+
+    // Returns the thread used for compositor workers. This creates a new thread if a
+    // thread doesn't already exist.
+    WebThreadSupportingGC& compositorWorkerThread();
+
+    // Attempts to initialize/shutdown a thread if necessary. Does nothing if the thread
+    // is already initialized, or if the thread has more than one active workers at the
+    // time of shutdown.
+    void initializeBackingThread();
+    void shutdownBackingThread();
+
+    PassOwnPtr<WorkerV8Isolate> createIsolate();
+    void willDestroyIsolate();
+    void destroyIsolate();
+    void terminateIsolate();
+
+private:
+    CompositorWorkerManager();
+    ~CompositorWorkerManager();
+
+    Mutex m_mutex;
+    OwnPtr<WebThreadSupportingGC> m_thread;
+    int m_workerCount = 0;
+    OwnPtr<WorkerV8Isolate> m_isolate;
+    int m_isolateCount = 0;

[kinuko, 2015/05/31 15:18:24]

Using manual counters is not great especially if we have two of them... in the
current interface it's not straightforward but could we somehow bundle them at
least in this class? (We may need to break them later if we break the tie
between thread and isolate, but changing it wouldn't be that hard if it's only
for CWManager)

[sadrul, 2015/06/01 05:24:11]

Done.

+};
+
+} // namespace blink
+
+#endif // CompositorWorkerManager_h