Fix two semantic errors from my previous check-in.

runtime/vm/dart_api_impl.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 "include/dart_api.h"
 
 #include "vm/bigint_operations.h"
 #include "vm/class_finalizer.h"
 #include "vm/compiler.h"
 #include "vm/dart.h"
@@ skipping 1613 matching lines @@
   if (bytes == NULL) {
     return Api::NewError("%s expects argument 'bytes' to be non-null.",
                          CURRENT_FUNC);
   }
   if (length == NULL) {
     return Api::NewError("%s expects argument 'length' to be non-null.",
                         CURRENT_FUNC);
   }
   const char* cstring = str.ToCString();
   *length = Utf8::Length(str);
-  char* result = reinterpret_cast<char*>(Api::Allocate(isolate, *length));
+  uint8_t* result = reinterpret_cast<uint8_t*>(Api::Allocate(isolate, *length));
   if (result == NULL) {
     return Api::NewError("Unable to allocate memory");
   }
   memmove(result, cstring, *length);
   *bytes = result;
   return Api::Success(isolate);
 }
 
 
 // --- Lists ---
@@ skipping 1677 matching lines @@
       *buffer = NULL;
     }
     delete debug_region;
   } else {
     *buffer = NULL;
     *buffer_size = 0;
   }
 }
 
 }  // namespace dart