Use NSS_DISABLE_UNLOAD in valgrind and heapcheck scripts to avoid unsymbolized backtraces.

tools/valgrind/valgrind_test.py

 #!/usr/bin/python
 # Copyright (c) 2011 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 # valgrind_test.py
 
 """Runs an exe through Valgrind and puts the intermediate files in a
 directory.
 """
@@ skipping 138 matching lines @@
 
   def Execute(self):
     """ Execute the app to be tested after successful instrumentation.
     Full execution command-line provided by subclassers via proc."""
     logging.info("starting execution...")
 
     proc = self.ToolCommand()
 
     add_env = {
       "G_SLICE" : "always-malloc",
+      "NSS_DISABLE_UNLOAD" : "1",
       "NSS_DISABLE_ARENA_FREE_LIST" : "1",
       "GTEST_DEATH_TEST_USE_FORK" : "1",
     }
     for k,v in add_env.iteritems():
       logging.info("export %s=%s", k, v)
       os.putenv(k, v)
 
     return common.RunSubprocess(proc, self._timeout)
 
   def RunTestsAndAnalyze(self, check_sanity):
@@ skipping 785 matching lines @@
       platform_name = sys.platform + "(Unknown)"
     raise RuntimeError, "Unknown tool (tool=%s, platform=%s)" % (tool_name,
                                                                  platform_name)
 
 def CreateTool(tool):
   return ToolFactory().Create(tool)
 
 if __name__ == '__main__':
   logging.error(sys.argv[0] + " can not be run from command line")
   sys.exit(1)