Fix a couple of isolate-related memory leaks that show up a lot in valgrind output.

runtime/lib/isolate.cc

 // Copyright (c) 2012, 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 "platform/assert.h"
 #include "vm/bootstrap_natives.h"
 #include "vm/class_finalizer.h"
 #include "vm/dart.h"
 #include "vm/dart_api_impl.h"
 #include "vm/dart_entry.h"
@@ skipping 178 matching lines @@
     const Array& kNoArgumentNames = Array::Handle();
     result = DartEntry::InvokeDynamic(target,
                                       target_function,
                                       arguments,
                                       kNoArgumentNames);
     if (result.IsError()) {
       ProcessError(result);
     }
     ASSERT(result.IsNull());
     free(class_name);
+    free(library_url);
     result = isolate->StandardRunLoop();
     if (result.IsError()) {
       ProcessError(result);
     }
     ASSERT(result.IsNull());
 
   } else {
     Zone zone(isolate);
     HandleScope handle_scope(isolate);
     const Error& error = Error::Handle(
@@ skipping 149 matching lines @@
   intptr_t send_id = Smi::CheckedHandle(arguments->At(0)).Value();
   intptr_t reply_id = Smi::CheckedHandle(arguments->At(1)).Value();
   // TODO(iposva): Allow for arbitrary messages to be sent.
   uint8_t* data = SerializeObject(Instance::CheckedHandle(arguments->At(2)));
 
   // TODO(turnidge): Throw an exception when the return value is false?
   PortMap::PostMessage(send_id, reply_id, Api::CastMessage(data));
 }
 
 }  // namespace dart