[webcrypto] Fix TODO regarding asynchronous completion of crypto operations.

Source/modules/crypto/CryptoResultImpl.h

Index: Source/modules/crypto/CryptoResultImpl.h
diff --git a/Source/modules/crypto/CryptoResultImpl.h b/Source/modules/crypto/CryptoResultImpl.h
index e8a1f5c87bbf26b5e2780ad686a05a7b24e36c9c..aa5428b0c0f870d61787d941a7bcfe6fc555eb67 100644
--- a/Source/modules/crypto/CryptoResultImpl.h
+++ b/Source/modules/crypto/CryptoResultImpl.h
@@ -31,10 +31,14 @@
 #ifndef CryptoResultImpl_h
 #define CryptoResultImpl_h
 
+#include "bindings/v8/DOMRequestState.h"
 #include "bindings/v8/ScriptPromise.h"
+#include "core/dom/ContextLifecycleObserver.h"
 #include "core/platform/CryptoResult.h"
 #include "public/platform/WebCrypto.h"
+#include "wtf/Assertions.h"
 #include "wtf/Forward.h"
+#include "wtf/Threading.h"
 
 namespace WebCore {
 
@@ -42,7 +46,7 @@ class ScriptPromiseResolver;
 
 // Wrapper around a Promise to notify completion of the crypto operation.
 // Platform cannot know about Promises which are declared in bindings.
-class CryptoResultImpl FINAL : public CryptoResult {
+class CryptoResultImpl FINAL : public CryptoResult, public ContextLifecycleObserver {
 public:
     ~CryptoResultImpl();
 
@@ -55,11 +59,25 @@ public:
     virtual void completeWithKeyPair(const blink::WebCryptoKey& publicKey, const blink::WebCryptoKey& privateKey) OVERRIDE;
 
 private:
-    explicit CryptoResultImpl(ScriptPromise);
+    CryptoResultImpl(ExecutionContext*, ScriptPromise);
     void finish();
+    void CheckValidThread() const;
+
+    // Override from ContextLifecycleObserver
+    virtual void contextDestroyed() OVERRIDE;
+
+    // Returns true if the ExecutionContext is still alive and running.
+    bool canCompletePromise() const;
+
+    void clearPromiseResolver();
 
     RefPtr<ScriptPromiseResolver> m_promiseResolver;
+    DOMRequestState m_requestState;
+
+#if !ASSERT_DISABLED
+    ThreadIdentifier m_owningThread;
     bool m_finished;
+#endif
 };
 
 } // namespace WebCore