A round of edits to make mirrors.dart more like our current working

runtime/vm/benchmark_test.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 "vm/benchmark_test.h"
 
 #include "bin/file.h"
 
 #include "platform/assert.h"
 
@@ skipping 22 matching lines @@
 
 
 //
 // Measure compile of all functions in dart core lib classes.
 //
 BENCHMARK(CorelibCompileAll) {
   Timer timer(true, "Compile all of Core lib benchmark");
   timer.Start();
   const Error& error = Error::Handle(benchmark->isolate(),
                                      Library::CompileAll());
+  if (!error.IsNull()) {
+    OS::PrintErr("Unexpected error in CorelibCompileAll benchmark:\n%s",
+                 error.ToErrorCString());
+  }
   EXPECT(error.IsNull());
   timer.Stop();
   int64_t elapsed_time = timer.TotalElapsedTime();
   benchmark->set_score(elapsed_time);
 }
 
 #endif  // TARGET_ARCH_IA32 || TARGET_ARCH_X64
 
 
 //
@@ skipping 292 matching lines @@
   Dart_Handle cls = Dart_GetClass(lib, Dart_NewString("StackFrameTest"));
   Dart_Handle result = Dart_Invoke(cls, Dart_NewString("testMain"), 0, NULL);
   EXPECT_VALID(result);
   int64_t elapsed_time = 0;
   result = Dart_IntegerToInt64(result, &elapsed_time);
   EXPECT_VALID(result);
   benchmark->set_score(elapsed_time);
 }
 
 }  // namespace dart