Revert "Verify that FetchEvent::m_request holds same-thread reference."

Undo r440475's temporary use of SameThreadCheckedMember<>.

R=
BUG=655926

Review-Url: https://codereview.chromium.org/2629613002
Cr-Commit-Position: refs/heads/master@{#443257}

third_party/WebKit/Source/modules/serviceworkers/FetchEvent.h

@@ -74,8 +74,7 @@ class MODULES_EXPORT FetchEvent final : public ExtendableEvent {
 
  private:
   Member<RespondWithObserver> m_observer;
-  // TODO(sof): remove once crbug.com/655926 has been diagnosed.
-  SameThreadCheckedMember<Request> m_request;
+  Member<Request> m_request;
   Member<PreloadResponseProperty> m_preloadResponseProperty;
   String m_clientId;
   bool m_isReload;