Issue #2678 - Stop using EnsureExpandoObject in codegen code when we just want to preserver the wrapper for a DOM proxy.

dom/base/nsContentList.h

@@ -260,6 +260,7 @@ public:
 
   // nsWrapperCache
   using nsWrapperCache::GetWrapperPreserveColor;
+  using nsWrapperCache::PreserveWrapper;
   virtual JSObject* WrapObject(JSContext* aCx, JS::Handle<JSObject*> aGivenProto) override;
 protected:
   virtual ~nsContentList();
@@ -268,6 +269,10 @@ protected:
   {
     return nsWrapperCache::GetWrapperPreserveColor();
   }
+  virtual void PreserveWrapperInternal(nsISupports* aScriptObjectHolder) override
+  {
+    nsWrapperCache::PreserveWrapper(aScriptObjectHolder);
+  }
 public:
 
   // nsIDOMHTMLCollection

dom/bindings/Codegen.py

@@ -3708,17 +3708,6 @@ class CGWrapWithCacheMethod(CGAbstractMethod):
         self.properties = properties
 
     def definition_body(self):
-        if self.descriptor.proxy:
-            preserveWrapper = dedent(
-                """
-                // For DOM proxies, the only reliable way to preserve the wrapper
-                // is to force creation of the expando object.
-                JS::Rooted<JSObject*> unused(aCx,
-                  DOMProxyHandler::EnsureExpandoObject(aCx, aReflector));
-                """)
-        else:
-            preserveWrapper = "PreserveWrapper(aObject);\n"
-
         failureCode = dedent(
             """
             aCache->ReleaseWrapper(aObject);
@@ -3773,7 +3762,7 @@ class CGWrapWithCacheMethod(CGAbstractMethod):
             // somewhat common) to have a non-null aGivenProto which is the
             // same as canonicalProto.
             if (proto != canonicalProto) {
-              $*{preserveWrapper}
+              PreserveWrapper(aObject);
             }
 
             return true;
@@ -3785,8 +3774,7 @@ class CGWrapWithCacheMethod(CGAbstractMethod):
                                                             failureCode),
             slots=InitMemberSlots(self.descriptor, failureCode),
             setImmutablePrototype=SetImmutablePrototype(self.descriptor,
-                                                        failureCode),
+                                                        failureCode))
-            preserveWrapper=preserveWrapper)
 
 
 class CGWrapMethod(CGAbstractMethod):

dom/html/HTMLFormControlsCollection.h

@@ -78,6 +78,7 @@ public:
 
   // nsWrapperCache
   using nsWrapperCache::GetWrapperPreserveColor;
+  using nsWrapperCache::PreserveWrapper;
   virtual JSObject* WrapObject(JSContext* aCx, JS::Handle<JSObject*> aGivenProto) override;
 protected:
   virtual ~HTMLFormControlsCollection();
@@ -85,6 +86,10 @@ protected:
   {
     return nsWrapperCache::GetWrapperPreserveColor();
   }
+  virtual void PreserveWrapperInternal(nsISupports* aScriptObjectHolder) override
+  {
+    nsWrapperCache::PreserveWrapper(aScriptObjectHolder);
+  }
 public:
 
   static bool ShouldBeInElements(nsIFormControl* aFormControl);

dom/html/HTMLOptionsCollection.h

@@ -44,6 +44,7 @@ public:
   // nsWrapperCache
   using nsWrapperCache::GetWrapperPreserveColor;
   using nsWrapperCache::GetWrapper;
+  using nsWrapperCache::PreserveWrapper;
   virtual JSObject* WrapObject(JSContext* aCx, JS::Handle<JSObject*> aGivenProto) override;
 protected:
   virtual ~HTMLOptionsCollection() = default;
@@ -52,6 +53,10 @@ protected:
   {
     return nsWrapperCache::GetWrapperPreserveColor();
   }
+  virtual void PreserveWrapperInternal(nsISupports* aScriptObjectHolder) override
+  {
+    nsWrapperCache::PreserveWrapper(aScriptObjectHolder);
+  }
 public:
 
   // nsIDOMHTMLOptionsCollection interface

dom/html/HTMLTableElement.cpp

@@ -48,6 +48,7 @@ public:
 
   // nsWrapperCache
   using nsWrapperCache::GetWrapperPreserveColor;
+  using nsWrapperCache::PreserveWrapper;
   virtual JSObject* WrapObject(JSContext* aCx, JS::Handle<JSObject*> aGivenProto) override;
 protected:
   virtual ~TableRowsCollection();
@@ -56,6 +57,10 @@ protected:
   {
     return nsWrapperCache::GetWrapperPreserveColor();
   }
+  virtual void PreserveWrapperInternal(nsISupports* aScriptObjectHolder) override
+  {
+    nsWrapperCache::PreserveWrapper(aScriptObjectHolder);
+  }
 
   // Those rows that are not in table sections
   HTMLTableElement* mParent;

dom/html/nsIHTMLCollection.h

@@ -85,9 +85,16 @@ public:
     }
     return obj;
   }
+  void PreserveWrapper(nsISupports* aScriptObjectHolder)
+  {
+    PreserveWrapperInternal(aScriptObjectHolder);
+  }
   virtual JSObject* WrapObject(JSContext* aCx, JS::Handle<JSObject*> aGivenProto) = 0;
 protected:
+  // Hook for calling nsWrapperCache::GetWrapperPreserveColor.
   virtual JSObject* GetWrapperPreserveColorInternal() = 0;
+  // Hook for calling nsWrapperCache::PreserveWrapper.
+  virtual void PreserveWrapperInternal(nsISupports* aScriptObjectHolder) = 0;
 };
 
 NS_DEFINE_STATIC_IID_ACCESSOR(nsIHTMLCollection, NS_IHTMLCOLLECTION_IID)