Don't flatten every time we call CharCodeAt

src/runtime.cc

Index: src/runtime.cc
diff --git a/src/runtime.cc b/src/runtime.cc
index b32ae8a1b4b81a85c4d8e0d1737eea1b367d61b3..c12c71d8ec112c5ae81edb1d909967f0a1616b1b 100644
--- a/src/runtime.cc
+++ b/src/runtime.cc
@@ -2060,20 +2060,11 @@ RUNTIME_FUNCTION(MaybeObject*, Runtime_StringCharCodeAt) {
     i = static_cast<uint32_t>(DoubleToInteger(value));
   }
 
-  // Flatten the string.  If someone wants to get a char at an index
-  // in a cons string, it is likely that more indices will be
-  // accessed.
-  Object* flat;
-  { MaybeObject* maybe_flat = subject->TryFlatten();
-    if (!maybe_flat->ToObject(&flat)) return maybe_flat;
-  }
-  subject = String::cast(flat);
-
   if (i >= static_cast<uint32_t>(subject->length())) {
     return isolate->heap()->nan_value();
   }
 
-  return Smi::FromInt(subject->Get(i));
+  return subject->GetMayFlatten(i);
 }
 
 
@@ -3636,9 +3627,8 @@ RUNTIME_FUNCTION(MaybeObject*, Runtime_NumberToPrecision) {
 // string->Get(index).
 static Handle<Object> GetCharAt(Handle<String> string, uint32_t index) {
   if (index < static_cast<uint32_t>(string->length())) {
-    string->TryFlatten();
     return LookupSingleCharacterStringFromCode(
-        string->Get(index));
+        StringGetMayFlatten(string, index));
   }
   return Execution::CharAt(string, index);
 }