[Sync] Fix a subtle use-after-free in Attachments.

tools/valgrind/memcheck/suppressions.txt

Index: tools/valgrind/memcheck/suppressions.txt
diff --git a/tools/valgrind/memcheck/suppressions.txt b/tools/valgrind/memcheck/suppressions.txt
index d856a81ce45acd005a428a63ea9cf10e0c817093..1fefb6154d1b9cca639c745fddf3c6cfd9a93de6 100644
--- a/tools/valgrind/memcheck/suppressions.txt
+++ b/tools/valgrind/memcheck/suppressions.txt
@@ -3154,15 +3154,3 @@
    fun:_ZN4base26PostTaskAndReplyWithResultIN3net20WifiPHYLayerProtocolES2_EEbPNS*
    fun:_ZN7metrics22NetworkMetricsProvider25ProbeWifiPHYLayerProtocolEv
 }
-{
-   bug_603275
-   Memcheck:Unaddressable
-   fun:_ZNKSs4sizeEv
-   fun:_ZSteqIcEN9__gnu_cxx11__enable_ifIXsr9__is_charIT_EE7__valueEbE6__typeERKSbIS2_St11char_traitsIS2_ESaIS2_EESA_
-   fun:_ZNKSt8equal_toISsEclERKSsS2_
-   fun:_ZNKSt8__detail15_Hash_code_baseISsSt4pairIKSsSt10unique_ptrIN6syncer24AttachmentDownloaderImpl13DownloadState*
-   fun:_ZNSt10_HashtableISsSt4pairIKSsSt10unique_ptrIN6syncer24AttachmentDownloaderImpl13DownloadStateESt14default*
-   fun:_ZN6syncer24AttachmentDownloaderImpl17OnGetTokenFailureEPKN18OAuth2TokenService7RequestERK22GoogleServiceAuthError
-   fun:_ZThn8_N6syncer24AttachmentDownloaderImpl17OnGetTokenFailureEPKN18OAuth2TokenService7RequestERK22GoogleServiceAuthError
-   fun:_ZN12_GLOBAL__N_111RequestCore28InformOwnerOnGetTokenFailureE22GoogleServiceAuthError
-}