Fix use after free bug in PprofCodeObserver.

runtime/vm/os_linux.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/os.h"
 
 #include <errno.h>
 #include <limits.h>
 #include <malloc.h>
 #include <time.h>
@@ skipping 94 matching lines @@
       return;
     }
     const char* filename = FLAG_generate_pprof_symbols;
     void* out_file = (*file_open)(filename);
     ASSERT(out_file != NULL);
     DebugInfo::ByteBuffer* debug_region = new DebugInfo::ByteBuffer();
     ASSERT(debug_region != NULL);
     pprof_symbol_generator_->WriteToMemory(debug_region);
     int buffer_size = debug_region->size();
     void* buffer = debug_region->data();
-    delete debug_region;
     if (buffer_size > 0) {
       ASSERT(buffer != NULL);
       (*file_write)(buffer, buffer_size, out_file);
     }
+    delete debug_region;
     (*file_close)(out_file);
     DebugInfo::UnregisterAllSections();
   }
 
   virtual bool IsActive() const {
     return FLAG_generate_pprof_symbols != NULL;
   }
 
   virtual void Notify(const char* name,
                       uword base,
@@ skipping 270 matching lines @@
 void OS::Abort() {
   abort();
 }
 
 
 void OS::Exit(int code) {
   exit(code);
 }
 
 }  // namespace dart