suppress memory leak from ValueStoreFrontend

TBR=koz@chromium.org
BUG=175823
TEST=waterfall.sh

Review URL: https://codereview.chromium.org/12218129

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@182057 0039d316-1c4b-4281-b951-d872f2087c98

tools/valgrind/memcheck/suppressions.txt

@@ -6525,3 +6525,9 @@
    fun:_ZN4base15DictionaryValue6RemoveERKSsPPNS_5ValueE
    fun:_ZN32PluginFinderTest_JsonSyntax_Test8TestBodyEv
 }
+{
+   bug_175823
+   Memcheck:Leak
+   ...
+   fun:_ZN18ValueStoreFrontend*
+}