Fix bogus unreachable in debug code.

src/hydrogen.cc

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 3878 matching lines @@
     case JSObject::EXTERNAL_UNSIGNED_SHORT_ELEMENTS:
     case JSObject::EXTERNAL_INT_ELEMENTS:
     case JSObject::EXTERNAL_UNSIGNED_INT_ELEMENTS: {
       HToInt32* floor_val = new(zone()) HToInt32(val);
       AddInstruction(floor_val);
       val = floor_val;
       break;
     }
     case JSObject::EXTERNAL_FLOAT_ELEMENTS:
     case JSObject::EXTERNAL_DOUBLE_ELEMENTS:
+      break;
+
     case JSObject::FAST_ELEMENTS:
     case JSObject::FAST_DOUBLE_ELEMENTS:
     case JSObject::DICTIONARY_ELEMENTS:
       UNREACHABLE();
       break;
   }
   return new(zone()) HStoreKeyedSpecializedArrayElement(
       external_elements,
       checked_key,
       val,
@@ skipping 2489 matching lines @@
     }
   }
 
 #ifdef DEBUG
   if (graph_ != NULL) graph_->Verify();
   if (allocator_ != NULL) allocator_->Verify();
 #endif
 }
 
 } }  // namespace v8::internal