Explicitly track the lifecycle of PendingScript.

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

 /*
  * Copyright (C) 2010 Google, 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 72 matching lines @@
   void MarkParserBlockingLoadStartTime();
   // Returns the time the load of this script started blocking the parser, or
   // zero if this script hasn't yet blocked the parser, in
   // monotonicallyIncreasingTime.
   double ParserBlockingLoadStartTime() const {
     return parser_blocking_load_start_time_;
   }
 
   void WatchForLoad(PendingScriptClient*);
   void StopWatchingForLoad();
+  bool WatchingForLoad() const { return client_; }
 
   ScriptElementBase* GetElement() const;
 
   DECLARE_TRACE();
 
   ClassicScript* GetSource(const KURL& document_url,
                            bool& error_occurred) const;
 
   void SetStreamer(ScriptStreamer*);
   void StreamingFinished();
 
-  bool IsReady() const;
-  bool ErrorOccurred() const;
+  bool IsReady() const {
+    CheckState();
+    return ready_state_ >= kReady;
+  }
+  bool ErrorOccurred() const {
+    CheckState();
+    return ready_state_ == kErrorOccurred;
+  }
 
   void StartStreamingIfPossible(Document*, ScriptStreamer::Type);
   void Dispose();
 
  private:
   PendingScript(ScriptElementBase*,
                 ScriptResource*,
                 const TextPosition&,
                 bool is_for_testing = false);
   PendingScript() = delete;
 
   void CheckState() const;
 
   // ScriptResourceClient
   void NotifyFinished(Resource*) override;
   String DebugName() const override { return "PendingScript"; }
   void NotifyAppendData(ScriptResource*) override;
 
   // MemoryCoordinatorClient
   void OnPurgeMemory() override;
 
-  bool watching_for_load_;
+  enum ReadyState {
+    // These states are considered "not ready".
+    kWaitingForResource,
+    kWaitingForStreaming,
+    // These states are considered "ready".
+    kReady,
+    kErrorOccurred,
+  };
+
+  // Advances the current state of the script, reporting to the client is

[hiroshige, 2017/04/24 19:16:53]

nit: reporting to the client *if*?

[jbroman, 2017/05/01 15:08:02]

Done.

+  // appropriate.
+  void AdvanceReadyState(ReadyState);
+
+  ReadyState ready_state_;
 
   // |m_element| must points to the corresponding ScriptLoader's
   // ScriptElementBase and thus must be non-null before dispose() is called
   // (except for unit tests).
   Member<ScriptElementBase> element_;
 
   TextPosition starting_position_;  // Only used for inline script tags.
   bool integrity_failure_;
   double parser_blocking_load_start_time_;
 
   Member<ScriptStreamer> streamer_;
   Member<PendingScriptClient> client_;
 
   // This flag is used to skip non-null checks of |m_element| in unit
   // tests, because |m_element| can be null in unit tests.
   const bool is_for_testing_;
 };
 
 }  // namespace blink
 
 #endif  // PendingScript_h