suppress memory leak from PluginFinderTest_JsonSyntax_Test

tools/valgrind/memcheck/suppressions.txt

 # There are four kinds of suppressions in this file.
 # 1. third party stuff we have no control over
 #
 # 2. intentional unit test errors, or stuff that is somehow a false positive
 # in our own code, or stuff that is so trivial it's not worth fixing
 #
 # 3. Suppressions for real chromium bugs that are not yet fixed.
 # These should all be in chromium's bug tracking system (but a few aren't yet).
 # Periodically we should sweep this file and the bug tracker clean by
 # running overnight and removing outdated bugs/suppressions.
@@ skipping 6497 matching lines @@
    fun:_ZN3gpu5gles2*Immediate4InitE*
    fun:_ZN3gpu5gles2*GLES2ImplementationTest_*_Test8TestBodyEv
 }
 {
    bug_175100
    Memcheck:Leak
    ...
    fun:_ZN20OneClickSigninHelper14DidStopLoadingEPN7content14RenderViewHostE
    fun:_ZN67OneClickSigninHelperTest_SigninFromWebstoreWithConfigSyncfirst_Test8TestBodyEv
 }
+{
+   bug_175815
+   Memcheck:Leak
+   fun:_Znw*
+   fun:_ZN4base5Value18CreateIntegerValueEi
+   fun:_ZNK4base16FundamentalValue8DeepCopyEv
+   fun:_ZN4base8internal12_GLOBAL__N_125DictionaryHiddenRootValue26RemoveWithoutPathExpansionERKSsPPNS_5ValueE
+   fun:_ZN4base15DictionaryValue6RemoveERKSsPPNS_5ValueE
+   fun:_ZN32PluginFinderTest_JsonSyntax_Test8TestBodyEv
+}