[crankshaft] Re-add fast-case for string add left/right.

src/code-stubs.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/code-stubs.h"
 
 #include <sstream>
 
 #include "src/bootstrapper.h"
 #include "src/cpu-profiler.h"
@@ skipping 306 matching lines @@
 std::ostream& operator<<(std::ostream& os, const StringAddFlags& flags) {
   switch (flags) {
     case STRING_ADD_CHECK_NONE:
       return os << "CheckNone";
     case STRING_ADD_CHECK_LEFT:
       return os << "CheckLeft";
     case STRING_ADD_CHECK_RIGHT:
       return os << "CheckRight";
     case STRING_ADD_CHECK_BOTH:
       return os << "CheckBoth";
+    case STRING_ADD_CONVERT_LEFT:
+      return os << "ConvertLeft";
+    case STRING_ADD_CONVERT_RIGHT:
+      return os << "ConvertRight";
+    case STRING_ADD_CONVERT:
+      break;
   }
   UNREACHABLE();
   return os;
 }
 
 
 void StringAddStub::PrintBaseName(std::ostream& os) const {  // NOLINT
   os << "StringAddStub_" << flags() << "_" << pretenure_flag();
 }
 
@@ skipping 712 matching lines @@
 
   if (type->Is(Type::UntaggedPointer())) {
     return Representation::External();
   }
 
   DCHECK(!type->Is(Type::Untagged()));
   return Representation::Tagged();
 }
 }  // namespace internal
 }  // namespace v8