Free worker context resources on idle.

cc/output/context_provider.h

Index: cc/output/context_provider.h
diff --git a/cc/output/context_provider.h b/cc/output/context_provider.h
index 2245b643e134b464d0db441cd4bd5dfae0ca2d2e..34db04b3564e4c9b8018f74239f08510dbed714d 100644
--- a/cc/output/context_provider.h
+++ b/cc/output/context_provider.h
@@ -12,6 +12,7 @@
 #include "base/memory/ref_counted.h"
 #include "base/synchronization/lock.h"
 #include "cc/base/cc_export.h"
+#include "gpu/command_buffer/client/context_support.h"
 #include "gpu/command_buffer/common/capabilities.h"
 
 class GrContext;
@@ -35,18 +36,10 @@ class ContextProvider : public base::RefCountedThreadSafe<ContextProvider> {
   // lock from GetLock(), so is not always supported. Most use of
   // ContextProvider should be single-thread only on the thread that
   // BindToCurrentThread is run on.
-  class ScopedContextLock {
+  class CC_EXPORT ScopedContextLock {
    public:
-    explicit ScopedContextLock(ContextProvider* context_provider)
-        : context_provider_(context_provider),
-          context_lock_(*context_provider_->GetLock()) {
-      // Allow current thread to use |context_provider_|.
-      context_provider_->DetachFromThread();
-    }
-    ~ScopedContextLock() {
-      // Allow usage by thread for which |context_provider_| is bound to.
-      context_provider_->DetachFromThread();
-    }
+    explicit ScopedContextLock(ContextProvider* context_provider);
+    ~ScopedContextLock();
 
     gpu::gles2::GLES2Interface* ContextGL() {
       return context_provider_->ContextGL();
@@ -55,6 +48,7 @@ class ContextProvider : public base::RefCountedThreadSafe<ContextProvider> {
    private:
     ContextProvider* const context_provider_;
     base::AutoLock context_lock_;
+    std::unique_ptr<gpu::ContextSupport::ScopedBusy> busy_;
   };
 
   // Bind the 3d context to the current thread. This should be called before