Implement value printer to prevent Valgrind errors in AudioPowerMonitor unit tests.

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 # running overnight and removing outdated bugs/suppressions.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 7369 matching lines @@
    fun:_Znw*
    ...
    fun:_ZN3sql10Connection18GetCachedStatementERKNS_11StatementIDEPKc
    ...
    fun:_ZN15webkit_database15DatabaseTracker23UpgradeToCurrentVersionEv
    fun:_ZN15webkit_database15DatabaseTracker8LazyInitEv
    fun:_ZN15webkit_database15DatabaseTracker23GetAllOriginIdentifiersEPSt6vectorISsSaISsEE
    fun:_ZN15webkit_database12_GLOBAL__N_120GetOriginsOnDBThreadEPNS_15DatabaseTrackerEPSt3setI4GURLSt4lessIS4_ESaIS4_EE
 }
 {
-   bug_263315
-   Memcheck:Uninitialized
-   ...
-   fun:snprintf
-   ...
-   fun:_ZN7testing13PrintToStringIN5media12_GLOBAL__N_112TestScenarioEEESsRKT_
-   fun:_ZN7testing8internal25ParameterizedTestCaseInfoIN5media21AudioPowerMonitorTestEE13RegisterTestsEv
-}
-{
    quic_socket_utils_write_packet_msg_name
    Memcheck:Param
    socketcall.sendmsg(msg.msg_name)
    obj:/lib/x86_64-linux-gnu/libpthread-2.15.so
    fun:_ZN3net5tools15QuicSocketUtils11WritePacketEiPKcmRKSt6vectorIhSaIhEERKNS_10IPEndPointEPi
    ...
 }
 {
    quic_socket_utils_write_packet_msg_control
    Memcheck:Param
    socketcall.sendmsg(msg.msg_control)
    obj:/lib/x86_64-linux-gnu/libpthread-2.15.so
    fun:_ZN3net5tools15QuicSocketUtils11WritePacketEiPKcmRKSt6vectorIhSaIhEERKNS_10IPEndPointEPi
    ...
 }