Bug 1295370 - Stop lazily creating the root node in nsTextEditorState::GetRootFrame. r=ehsan

AFAICT this doesn't change behavior, since all the callers of GetRootNode should
occur after we've already called BindToFrame. However, it makes it easier for
future static analysis to see that we don't trigger node creation from
nsTextControlFrame::AppendAnonymousContentTo.

dom/html/nsTextEditorState.cpp

@@ -1157,9 +1157,11 @@ nsTextEditorState::BindToFrame(nsTextControlFrame* aFrame)
 
   mBoundFrame = aFrame;
 
-  nsIContent *rootNode = GetRootNode();
+  nsresult rv = CreateRootNode();
+  NS_ENSURE_SUCCESS(rv, rv);
 
-  nsresult rv = InitializeRootNode();
+  nsIContent *rootNode = GetRootNode();
+  rv = InitializeRootNode();
   NS_ENSURE_SUCCESS(rv, rv);
 
   nsIPresShell *shell = mBoundFrame->PresContext()->GetPresShell();
@@ -1753,8 +1755,8 @@ nsTextEditorState::UnbindFromFrame(nsTextControlFrame* aFrame)
 nsresult
 nsTextEditorState::CreateRootNode()
 {
-  NS_ENSURE_TRUE(!mRootNode, NS_ERROR_UNEXPECTED);
-  NS_ENSURE_ARG_POINTER(mBoundFrame);
+  MOZ_ASSERT(!mRootNode);
+  MOZ_ASSERT(mBoundFrame);
 
   nsIPresShell *shell = mBoundFrame->PresContext()->GetPresShell();
   NS_ENSURE_TRUE(shell, NS_ERROR_FAILURE);

dom/html/nsTextEditorState.h

@@ -163,8 +163,6 @@ public:
   nsresult CreatePlaceholderNode();
 
   mozilla::dom::Element* GetRootNode() {
-    if (!mRootNode)
-      CreateRootNode();
     return mRootNode;
   }
   mozilla::dom::Element* GetPlaceholderNode() {