Update from https://crrev.com/316786

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 7362e8b55aa9acffd62060af1ed08c766581c4f2..71d06bd7591d22f180f7a395b5be412d733b03bb 100644
--- a/cc/output/context_provider.h
+++ b/cc/output/context_provider.h
@@ -12,6 +12,10 @@
 
 class GrContext;
 
+namespace base {
+class Lock;
+}
+
 namespace gpu {
 class ContextSupport;
 namespace gles2 { class GLES2Interface; }
@@ -27,6 +31,7 @@ class ContextProvider : public base::RefCountedThreadSafe<ContextProvider> {
   // Once this function has been called, the class should only be accessed
   // from the same thread.
   virtual bool BindToCurrentThread() = 0;
+  virtual void DetachFromThread() {}
 
   virtual gpu::gles2::GLES2Interface* ContextGL() = 0;
   virtual gpu::ContextSupport* ContextSupport() = 0;
@@ -39,6 +44,13 @@ class ContextProvider : public base::RefCountedThreadSafe<ContextProvider> {
     CC_EXPORT Capabilities();
   };
 
+  // Sets up a lock so this context can be used from multiple threads.
+  virtual void SetupLock() = 0;
+
+  // Returns the lock that should be held if using this context from multiple
+  // threads.
+  virtual base::Lock* GetLock() = 0;
+
   // Returns the capabilities of the currently bound 3d context.
   virtual Capabilities ContextCapabilities() = 0;