Explicitly track the lifecycle of PendingScript.

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

Index: third_party/WebKit/Source/core/dom/PendingScript.h
diff --git a/third_party/WebKit/Source/core/dom/PendingScript.h b/third_party/WebKit/Source/core/dom/PendingScript.h
index 0be3dcfaacfa6df6aabdf69964b4fca89ff747e7..c45f845e2bd31c63801a7b4a081cf97898b4ebe8 100644
--- a/third_party/WebKit/Source/core/dom/PendingScript.h
+++ b/third_party/WebKit/Source/core/dom/PendingScript.h
@@ -90,6 +90,7 @@ class CORE_EXPORT PendingScript final
 
   void WatchForLoad(PendingScriptClient*);
   void StopWatchingForLoad();
+  bool WatchingForLoad() const { return client_; }
 
   ScriptElementBase* GetElement() const;
 
@@ -101,8 +102,14 @@ class CORE_EXPORT PendingScript final
   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();
@@ -124,7 +131,20 @@ class CORE_EXPORT PendingScript final
   // 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