Introduce runtime/platform directory for code shared between vm

runtime/bin/file_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 "bin/file.h"
 
+#include "platform/globals.h"
+
 #include "vm/assert.h"
-#include "vm/globals.h"
 #include "vm/unit_test.h"
 
 
 // Helper method to be able to run the test from the runtime
 // directory, or the top directory.
 static const char* GetFileName(const char* name) {
   if (File::Exists(name)) {
     return name;
   } else {
     static const int kRuntimeLength = strlen("runtime/");
@@ skipping 32 matching lines @@
   const char* kFilename =
       GetFileName("runtime/tests/vm/data/fixed_length_file");
   File* file = File::Open(kFilename, File::kRead);
   EXPECT(file != NULL);
   EXPECT(file->ReadFully(buf, 12));
   EXPECT_EQ(12, file->Position());
   EXPECT(file->ReadFully(buf, 6));
   EXPECT_EQ(18, file->Position());
   delete file;
 }