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

tools/valgrind/valgrind.sh

 #!/bin/bash
 
 # 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.
 
 # This is a small script for manually launching valgrind, along with passing
 # it the suppression file, and some helpful arguments (automatically attaching
 # the debugger on failures, etc).  Run it from your repo root, something like:
 #  $ sh ./tools/valgrind/valgrind.sh ./out/Debug/chrome
@@ skipping 73 matching lines @@
 echo "Using valgrind binaries from ${CHROME_VALGRIND}"
 
 set -x
 PATH="${CHROME_VALGRIND}/bin:$PATH"
 # We need to set these variables to override default lib paths hard-coded into
 # Valgrind binary.
 export VALGRIND_LIB="$CHROME_VALGRIND/lib/valgrind"
 export VALGRIND_LIB_INNER="$CHROME_VALGRIND/lib/valgrind"
 
 # G_SLICE=always-malloc: make glib use system malloc
+# NSS_DISABLE_UNLOAD=1: make nss skip dlclosing dynamically loaded modules,
+# which would result in "obj:*" in backtraces.
 # NSS_DISABLE_ARENA_FREE_LIST=1: make nss use system malloc
 # G_DEBUG=fatal_warnings: make  GTK abort on any critical or warning assertions.
 # If it crashes on you in the Options menu, you hit bug 19751,
 # comment out the G_DEBUG=fatal_warnings line.
 #
 # GTEST_DEATH_TEST_USE_FORK=1: make gtest death tests valgrind-friendly
 #
 # When everyone has the latest valgrind, we might want to add
 #  --show-possibly-lost=no
 # to ignore possible but not definite leaks.
 
 G_SLICE=always-malloc \
+NSS_DISABLE_UNLOAD=1 \
 NSS_DISABLE_ARENA_FREE_LIST=1 \
 G_DEBUG=fatal_warnings \
 GTEST_DEATH_TEST_USE_FORK=1 \
 $RUN_COMMAND \
   --trace-children=yes \
   --suppressions="$SUPPRESSIONS" \
   "${DEFAULT_TOOL_FLAGS[@]}" \
   "$@"