Turn IDBTransaction into the ContextLifecycleObserver it needs to be.

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

Index: third_party/WebKit/Source/core/dom/ContextLifecycleObserver.h
diff --git a/third_party/WebKit/Source/core/dom/ContextLifecycleObserver.h b/third_party/WebKit/Source/core/dom/ContextLifecycleObserver.h
index 3bf231d12754293cf4be7df0dacc5cc9bf55dc01..3bd070278fece042c53c06d3f8f9997c974fef87 100644
--- a/third_party/WebKit/Source/core/dom/ContextLifecycleObserver.h
+++ b/third_party/WebKit/Source/core/dom/ContextLifecycleObserver.h
@@ -42,6 +42,9 @@ class LocalFrame;
 // - 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;
@@ -90,6 +93,9 @@ class CORE_EXPORT ContextLifecycleObserver
 // - 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)