Reduce canonicalization when dragging

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

Index: third_party/WebKit/Source/core/editing/SelectionController.cpp
diff --git a/third_party/WebKit/Source/core/editing/SelectionController.cpp b/third_party/WebKit/Source/core/editing/SelectionController.cpp
index b53e47fc7df02c2823e0edb3b917245e9d536d6d..c253d60a8b364671d45f1bfe5f988ce3df32485e 100644
--- a/third_party/WebKit/Source/core/editing/SelectionController.cpp
+++ b/third_party/WebKit/Source/core/editing/SelectionController.cpp
@@ -387,6 +387,9 @@ void SelectionController::updateSelectionForMouseDrag(
   } else {
     basePosition = selection().computeVisibleSelectionInFlatTree().base();
   }
+  if (basePosition.isNull())

[yosin_UTC9, 2017/03/16 02:30:05]

Could you move this change in another patch?
with adding |DCHECK(basePosition.isNotNull())| in |applySelectAll()|.

[yoichio, 2017/03/16 04:10:59]

This needs because of SelectionEditor change.
Somehow in L346-350, we get "valid" |targetPosition| but null 
 |basePosition|.
I'm suspicious about this code that we get VSinDOM first and 
 covert it to VSinFlat. We should get VSinFlat directly?
Anyway this should be done in another patch.

+    return;
+
   const SelectionInFlatTree& appliedSelection = applySelectAll(
       basePosition, targetPosition.deepEquivalent(), mousePressNode,
       dragStartPos, target, hitTestResult.localPoint());