Ensure clean layout before calling plainText() (flat tree version)

third_party/WebKit/Source/core/editing/iterators/TextIterator.cpp

Index: third_party/WebKit/Source/core/editing/iterators/TextIterator.cpp
diff --git a/third_party/WebKit/Source/core/editing/iterators/TextIterator.cpp b/third_party/WebKit/Source/core/editing/iterators/TextIterator.cpp
index 5cc04a2bce4a99d935bfcbbc1b3fa9d29d1b0319..238385e2c460f66a6cb440149332f43f8e3c8f64 100644
--- a/third_party/WebKit/Source/core/editing/iterators/TextIterator.cpp
+++ b/third_party/WebKit/Source/core/editing/iterators/TextIterator.cpp
@@ -1211,6 +1211,12 @@ String plainText(const EphemeralRange& range, TextIteratorBehaviorFlags behavior
 
 String plainText(const EphemeralRangeInFlatTree& range, TextIteratorBehaviorFlags behavior)
 {
+    // TODO(xiaochengh): Move this check and the DisallowTransitionScope to
+    // |createPlainText| after we have ensure that both versions of |plainText|
+    // are called with clean layout.
+    if (range.isNull())
+        return emptyString();
+    DocumentLifecycle::DisallowTransitionScope disallowTransition(range.startPosition().document()->lifecycle());
     return createPlainText<EditingInFlatTreeStrategy>(range, behavior);
 }