Support concatenating with zero-size arrays with DICTIONARY_ELEMENTS in Runtime_ArrayConcat.

src/runtime/runtime-array.cc

 // Copyright 2014 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/v8.h"
 
 #include "src/arguments.h"
 #include "src/runtime/runtime-utils.h"
 
 namespace v8 {
@@ skipping 832 matching lines @@
                   break;
                 }
                 int32_t int_value = Smi::cast(element)->value();
                 double_storage->set(j, int_value);
                 j++;
               }
               break;
             }
             case FAST_HOLEY_ELEMENTS:
             case FAST_ELEMENTS:
+            case DICTIONARY_ELEMENTS:
               DCHECK_EQ(0, length);
               break;
             default:
               UNREACHABLE();
           }
         }
         if (failure) break;
       }
     }
     if (!failure) {
@@ skipping 446 matching lines @@
 }
 
 
 RUNTIME_FUNCTION(RuntimeReference_FastOneByteArrayJoin) {
   SealHandleScope shs(isolate);
   DCHECK(args.length() == 2);
   return isolate->heap()->undefined_value();
 }
 }
 }  // namespace v8::internal