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..e7c2c90f96b4e024411441a5976e81793204f542 100644
--- a/third_party/WebKit/Source/core/editing/DOMSelection.cpp
+++ b/third_party/WebKit/Source/core/editing/DOMSelection.cpp
@@ -272,8 +272,17 @@ void DOMSelection::setBaseAndExtent(Node* baseNode,
     return;
   }
 
-  if (!baseNode || !extentNode)
+  // 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) {
     UseCounter::count(frame(), UseCounter::SelectionSetBaseAndExtentNull);
+    frame()->selection().clear();
+    return;
+  }
+  if (!extentNode) {
+    UseCounter::count(frame(), UseCounter::SelectionSetBaseAndExtentNull);
+    extentOffset = 0;
+  }
 
   if (!isValidForPosition(baseNode) || !isValidForPosition(extentNode))
     return;