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 79689699ab7321b56aa665fb1d521ff9f584e24a..f9a54e515331fbbfcf5f83fb2b2fa379f6ef930c 100644
--- a/third_party/WebKit/Source/core/editing/iterators/TextIterator.cpp
+++ b/third_party/WebKit/Source/core/editing/iterators/TextIterator.cpp
@@ -1210,6 +1210,12 @@ 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 ensured 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);
 }