selection.setBaseAndExtent with null should not crash.

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

Index: third_party/WebKit/Source/core/editing/DOMSelection.cpp
diff --git a/third_party/WebKit/Source/core/editing/DOMSelection.cpp b/third_party/WebKit/Source/core/editing/DOMSelection.cpp
index 91d8dbedd404b282866de9c7e0d5c0719ca87a62..54ef6a5887d621f10f10d9146e2f564a48ac576b 100644
--- a/third_party/WebKit/Source/core/editing/DOMSelection.cpp
+++ b/third_party/WebKit/Source/core/editing/DOMSelection.cpp
@@ -272,8 +272,16 @@ void DOMSelection::setBaseAndExtent(Node* baseNode,
     return;
   }
 
-  if (!baseNode || !extentNode)
+  if (!baseNode || !extentNode) {
     UseCounter::count(frame(), UseCounter::SelectionSetBaseAndExtentNull);
+    // TODO(editing-dev): Behavior on where base or extent is null is still
+    // under discussion: https://github.com/w3c/selection-api/issues/72
+    if (!baseNode) {

[yosin_UTC9, 2016/12/02 04:38:02]

It seems that dealing nullptr explicitly is more readable.

if (!baseNode) {
  UseCounter::count(frame(), UseCounter::SelectionSetBaseAndExtentNull);
  frame->selection().clear();
  return;
}

if (!extendNode) {
  UseCounter::count(frame(), UseCounter::SelectionSetBaseAndExtentNull);
  collapse(baseNode, baseOffset, exceptionState);
  return;
}

+      frame()->selection().clear();
+      return;
+    }
+    extentOffset = 0;
+  }
 
   if (!isValidForPosition(baseNode) || !isValidForPosition(extentNode))
     return;