net: Add fuzzer for HostResolverImpl.

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 # running overnight and removing outdated bugs/suppressions.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 2173 matching lines @@
    fun:_ZN5blink10PingLoader9loadImageEPNS_10LocalFrameERKNS_4KURLE
    fun:_ZN5blink15ResourceFetcher10fetchImageERNS_12FetchRequestE
    fun:_ZN5blink11ImageLoader19doUpdateFromElementEb
    fun:_ZN5blink11ImageLoader4Task3runEv
 }
 {
    bug_386418
    Memcheck:Leak
    fun:_Znw*
    fun:_ZN4base8internal20PostTaskAndReplyImpl16PostTaskAndReplyERKN15tracked_objects8LocationERKNS_8CallbackIF*
-   fun:_ZN4base10WorkerPool16PostTaskAndReplyERKN15tracked_objects8LocationERKNS_8CallbackIF*
+   fun:_ZN4base10TaskRunner16PostTaskAndReplyERKN15tracked_objects8LocationERKNS_8CallbackIF*
    fun:_ZN3net16HostResolverImpl16LoopbackProbeJob*
    fun:_ZN3net16HostResolverImpl*
 }
 {
    bug_388668
    Memcheck:Leak
    fun:_Znw*
    fun:_ZN20data_reduction_proxy69DataReductionProxyBypassStatsTest_isDataReductionProxyUnreachable_Test8TestBodyEv
 }
 {
@@ skipping 781 matching lines @@
 {
    bug_602964
    Memcheck:Leak
    fun:_Znw*
    fun:_ZN4base4BindIMNS_12_GLOBAL__N_121PostTaskAndReplyRelayEFvvEJNS_8internal17UnretainedWrapper*
    fun:_ZN4base8internal20PostTaskAndReplyImpl16PostTaskAndReplyERKN15tracked_objects8LocationERKNS*
    fun:_ZN4base10TaskRunner16PostTaskAndReplyERKN15tracked_objects8LocationERKNS_8CallbackIFvvELNS*
    fun:_ZN4base26PostTaskAndReplyWithResultIN3net20WifiPHYLayerProtocolES2_EEbPNS*
    fun:_ZN7metrics22NetworkMetricsProvider25ProbeWifiPHYLayerProtocolEv
 }