Fix BlobBytesConsumer state assumption on cancellation

BUG=666756
R=tyoshino@chromium.org

Review-Url: https://codereview.chromium.org/2572683002
Cr-Commit-Position: refs/heads/master@{#438118}

third_party/WebKit/Source/modules/fetch/BlobBytesConsumer.cpp

@@ -231,13 +231,7 @@ void BlobBytesConsumer::didFinishLoading(unsigned long identifier,
 
 void BlobBytesConsumer::didFail(const ResourceError& e) {
   if (e.isCancellation()) {
-    // |m_loader| can be canceled when
-    //  - this object explicitly cancels it, or
-    //  - the global context is shutting down.
-    // In the first case, |m_state| should be Closed.
-    if (getExecutionContext() && !getExecutionContext()->isContextDestroyed())
-      DCHECK_EQ(PublicState::Closed, m_state);
-    if (m_state == PublicState::Closed)
+    if (m_state != PublicState::ReadableOrWaiting)
       return;
   }
   DCHECK_EQ(PublicState::ReadableOrWaiting, m_state);