Bug 1116714 part 2 - Don't create a frame for the custom content container when it has no children. r=roc

dom/base/nsDocument.cpp

@@ -5252,6 +5252,7 @@ nsIDocument::InsertAnonymousContent(Element& aElement, ErrorResult& aRv)
     return nullptr;
   }
 
+  nsAutoScriptBlocker scriptBlocker;
   nsCOMPtr<Element> container = shell->GetCanvasFrame()
                                      ->GetCustomContentContainer();
   if (!container) {
@@ -5276,6 +5277,8 @@ nsIDocument::InsertAnonymousContent(Element& aElement, ErrorResult& aRv)
     new AnonymousContent(clonedElement->AsElement());
   mAnonymousContents.AppendElement(anonymousContent);
 
+  shell->GetCanvasFrame()->ShowCustomContentContainer();
+
   return anonymousContent.forget();
 }
 
@@ -5289,6 +5292,7 @@ nsIDocument::RemoveAnonymousContent(AnonymousContent& aContent,
     return;
   }
 
+  nsAutoScriptBlocker scriptBlocker;
   nsCOMPtr<Element> container = shell->GetCanvasFrame()
                                      ->GetCustomContentContainer();
   if (!container) {
@@ -5314,6 +5318,9 @@ nsIDocument::RemoveAnonymousContent(AnonymousContent& aContent,
       break;
     }
   }
+  if (mAnonymousContents.IsEmpty()) {
+    shell->GetCanvasFrame()->HideCustomContentContainer();
+  }
 }
 
 //

layout/generic/nsCanvasFrame.cpp

@@ -53,6 +53,24 @@ NS_QUERYFRAME_HEAD(nsCanvasFrame)
   NS_QUERYFRAME_ENTRY(nsIAnonymousContentCreator)
 NS_QUERYFRAME_TAIL_INHERITING(nsContainerFrame)
 
+void
+nsCanvasFrame::ShowCustomContentContainer()
+{
+  if (mCustomContentContainer) {
+    mCustomContentContainer->UnsetAttr(kNameSpaceID_None, nsGkAtoms::hidden, true);
+  }
+}
+
+void
+nsCanvasFrame::HideCustomContentContainer()
+{
+  if (mCustomContentContainer) {
+    mCustomContentContainer->SetAttr(kNameSpaceID_None, nsGkAtoms::hidden,
+                                     NS_LITERAL_STRING("true"),
+                                     true);
+  }
+}
+
 nsresult
 nsCanvasFrame::CreateAnonymousContent(nsTArray<ContentInfo>& aElements)
 {
@@ -126,6 +144,11 @@ nsCanvasFrame::CreateAnonymousContent(nsTArray<ContentInfo>& aElements)
     mCustomContentContainer->AppendChildTo(node->AsContent(), true);
   }
 
+  // Only create a frame for mCustomContentContainer if it has some children.
+  if (len == 0) {
+    HideCustomContentContainer();
+  }
+
   return NS_OK;
 }
 

layout/generic/nsCanvasFrame.h

@@ -104,6 +104,18 @@ public:
     return mCustomContentContainer;
   }
 
+  /**
+   * Unhide the CustomContentContainer. This call only has an effect if
+   * mCustomContentContainer is non-null.
+   */
+  void ShowCustomContentContainer();
+
+  /**
+   * Hide the CustomContentContainer. This call only has an effect if
+   * mCustomContentContainer is non-null.
+   */
+  void HideCustomContentContainer();
+
   /** SetHasFocus tells the CanvasFrame to draw with focus ring
    *  @param aHasFocus true to show focus ring, false to hide it
    */