Bug 1360154 - Part 2. Add fast path to check whether valus is emtpy. r=masayuki

Actually, we use GetValue to check whether value is empty or not for placeholder.  But since GetValue uses TextEditor::OutputToString when on editor, it is expensive.  Since editor has DocumentIsEmpty method, we should use it for this case.

MozReview-Commit-ID: rQX8yjnWQz

--HG--
extra : rebase_source : 25ec89385d704f5c4d2d0a15021c2a59b0201983

dom/html/nsTextEditorState.cpp

@@ -2682,6 +2682,23 @@ nsTextEditorState::SetValue(const nsAString& aValue, uint32_t aFlags)
   return true;
 }
 
+bool
+nsTextEditorState::HasNonEmptyValue()
+{
+  if (mEditor && mBoundFrame && mEditorInitialized &&
+      !mIsCommittingComposition) {
+    bool empty;
+    nsresult rv = mEditor->GetDocumentIsEmpty(&empty);
+    if (NS_SUCCEEDED(rv)) {
+      return !empty;
+    }
+  }
+
+  nsAutoString value;
+  GetValue(value, true);
+  return !value.IsEmpty();
+}
+
 void
 nsTextEditorState::InitializeKeyboardEventListeners()
 {
@@ -2765,11 +2782,11 @@ void
 nsTextEditorState::UpdateOverlayTextVisibility(bool aNotify)
 {
   nsAutoString value, previewValue;
-  GetValue(value, true);
+  bool valueIsEmpty = !HasNonEmptyValue();
   GetPreviewText(previewValue);
 
-  mPreviewVisibility = value.IsEmpty() && !previewValue.IsEmpty();
-  mPlaceholderVisibility = value.IsEmpty() && previewValue.IsEmpty();
+  mPreviewVisibility = valueIsEmpty && !previewValue.IsEmpty();
+  mPlaceholderVisibility = valueIsEmpty && previewValue.IsEmpty();
 
   if (mPlaceholderVisibility &&
       !Preferences::GetBool("dom.placeholder.show_on_focus", true)) {

dom/html/nsTextEditorState.h

@@ -181,6 +181,11 @@ public:
   };
   MOZ_MUST_USE bool SetValue(const nsAString& aValue, uint32_t aFlags);
   void GetValue(nsAString& aValue, bool aIgnoreWrap) const;
+  bool HasNonEmptyValue();
+  // The following methods are for textarea element to use whether default
+  // value or not.
+  // XXX We might have to add assertion when it is into editable,
+  // or reconsider fixing bug 597525 to remove these.
   void EmptyValue() { if (mValue) mValue->Truncate(); }
   bool IsEmpty() const { return mValue ? mValue->IsEmpty() : true; }