Audit the use of updateStyleAndLayoutIgnorePendingStylesheets in canonicalPosition

third_party/WebKit/Source/core/editing/VisibleUnits.cpp

Index: third_party/WebKit/Source/core/editing/VisibleUnits.cpp
diff --git a/third_party/WebKit/Source/core/editing/VisibleUnits.cpp b/third_party/WebKit/Source/core/editing/VisibleUnits.cpp
index 64e14e90d098de8b049eb51b7e28470008ecdbf0..614178ba0be936f59d2554089fdf2b113e3db6e1 100644
--- a/third_party/WebKit/Source/core/editing/VisibleUnits.cpp
+++ b/third_party/WebKit/Source/core/editing/VisibleUnits.cpp
@@ -102,7 +102,7 @@ static PositionType canonicalPosition(const PositionType& passedPosition)
         return PositionType();
 
     DCHECK(position.document());
-    position.document()->updateStyleAndLayoutIgnorePendingStylesheets();
+    DCHECK(!position.document()->needsLayoutTreeUpdate());
 
     Node* node = position.computeContainerNode();
 
@@ -1240,6 +1240,13 @@ bool inSameLineAlgorithm(const PositionWithAffinityTemplate<Strategy>& position1
 {
     if (position1.isNull() || position2.isNull())
         return false;
+    if (position1.position().document() != position2.position().document())

[yosin_UTC9, 2016/09/12 09:25:03]

Could you change this to DCHEC_EQ(position1.position().document(),
position2.position().document())?

[Xiaocheng, 2016/09/12 11:20:49]

Done.

Haven't found any call site that may compare two positions in different
documents. And it's also weird if there is any.

+        return false;
+
+    // TODO(xiaochengh): The use of updateStyleAndLayoutIgnorePendingStylesheets
+    // needs to be audited.  See http://crbug.com/590369 for more details.
+    position1.position().document()->updateStyleAndLayoutIgnorePendingStylesheets();
+
     PositionWithAffinityTemplate<Strategy> startOfLine1 = startOfLine(position1);
     PositionWithAffinityTemplate<Strategy> startOfLine2 = startOfLine(position2);
     if (startOfLine1 == startOfLine2)