VM: Const-correctness fixes.

runtime/vm/custom_isolate_test.cc

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "include/dart_api.h"
 #include "include/dart_native_api.h"
 
 #include "vm/unit_test.h"
 
 // Custom Isolate Test.
@@ skipping 225 matching lines @@
   EXPECT_VALID(Dart_StringToCString(name, &name_str));
   if (strcmp(name_str, "native_echo") == 0) {
     return &native_echo;
   } else if (strcmp(name_str, "CustomIsolateImpl_start") == 0) {
     return &CustomIsolateImpl_start;
   }
   return NULL;
 }
 
 
-const char* saved_echo = NULL;
+char* saved_echo = NULL;
 static void native_echo(Dart_NativeArguments args) {
   Dart_EnterScope();
   Dart_Handle arg = Dart_GetNativeArgument(args, 0);
   Dart_Handle toString = Dart_ToString(arg);
   EXPECT_VALID(toString);
   const char* c_str = NULL;
   EXPECT_VALID(Dart_StringToCString(toString, &c_str));
   if (saved_echo) {
-    free(const_cast<char*>(saved_echo));
+    free(saved_echo);
   }
   saved_echo = strdup(c_str);
   OS::Print("-- (isolate=%p) %s\n", Dart_CurrentIsolate(), c_str);
   Dart_ExitScope();
 }
 
 
 static void CustomIsolateImpl_start(Dart_NativeArguments args) {
   OS::Print("-- Enter: CustomIsolateImpl_start --\n");
 
@@ skipping 77 matching lines @@
 
   OS::Print("-- Starting event loop --\n");
   Event* event = event_queue->Get();
   while (event) {
     event->Process();
     delete event;
     event = event_queue->Get();
   }
   OS::Print("-- Finished event loop --\n");
   EXPECT_STREQ("Received: 43", saved_echo);
-  free(const_cast<char*>(saved_echo));
+  free(saved_echo);
 
   delete event_queue;
   event_queue = NULL;
 }
 
 }  // namespace dart