Turn IDBTransaction into the ContextLifecycleObserver it needs to be.

third_party/WebKit/Source/core/dom/ContextLifecycleObserver.h

 /*
  * Copyright (C) 2008 Apple Inc. All Rights Reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 24 matching lines @@
 
 class LocalDOMWindow;
 class LocalFrame;
 
 // ContextClient and ContextLifecycleObserver are helpers to associate an
 // object with an ExecutionContext.
 //
 // - getExecutionContext() returns null after the context is detached.
 // - frame() is a syntax sugar for getExecutionContext()->frame(). It returns
 //   null after the context is detached or the context is not a Document.
+//
+// Both can safely be used up until destruction; i.e., unsafe to
+// call upon in a destructor.
 class CORE_EXPORT ContextClient : public GarbageCollectedMixin {
  public:
   ExecutionContext* getExecutionContext() const;
   LocalFrame* frame() const;
 
   DECLARE_VIRTUAL_TRACE();
 
  protected:
   explicit ContextClient(ExecutionContext*);
   explicit ContextClient(LocalFrame*);
@@ skipping 28 matching lines @@
  private:
   Type m_observerType;
 };
 
 // DOMWindowClient is a helper to associate an object with a LocalDOMWindow.
 //
 // - domWindow() returns null after the window is detached.
 // - frame() is a syntax sugar for domWindow()->frame(). It returns
 //   null after the window is detached.
 //
+// Both can safely be used up until destruction; i.e., unsafe to
+// call upon in a destructor.
+//
 // If the object is a per-ExecutionContext thing, use ContextClient/
 // ContextLifecycleObserver. If the object is a per-DOMWindow thing, use
 // DOMWindowClient. Basically, DOMWindowClient is expected to be used (only)
 // for objects directly held by LocalDOMWindow. Other objects should use
 // ContextClient/ContextLifecycleObserver.
 //
 // There is a subtle difference between the timing when the context gets
 // detached and the timing when the window gets detached. In common cases,
 // these two happen at the same timing. The only exception is a case where
 // a frame navigates from an initial empty document to another same-origin
@@ skipping 11 matching lines @@
   explicit DOMWindowClient(LocalDOMWindow*);
   explicit DOMWindowClient(LocalFrame*);
 
  private:
   WeakMember<LocalDOMWindow> m_domWindow;
 };
 
 }  // namespace blink
 
 #endif  // ContextLifecycleObserver_h