Avoid accessing uninitialized memory during DownloadManagerTest.

tools/valgrind/memcheck/suppressions_mac.txt

 # There are three kinds of suppressions in this file:
 # 1. Third party stuff we have no control over.
 #
 # 2. Intentional unit test errors, 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.
 # Periodically we should sweep this file and the bug tracker clean by
 # running overnight and removing outdated bugs/suppressions.
@@ skipping 2448 matching lines @@
 }
 {
    bug_148865
    Memcheck:Leak
    fun:_Znw*
    fun:_ZN16RenderThreadImpl4InitEv
    fun:_ZN16RenderThreadImplC2ERKSs
    fun:_ZN16RenderThreadImplC1ERKSs
    fun:_ZN21WebRTCAudioDeviceTest5SetUpEv
 }
-{
-   bug_150705
-   Memcheck:Uninitialized
-   ...
-   fun:_ZN7testing12_GLOBAL__N_126PrintByteSegmentInObjectToEPKhmmPSo
-   fun:_ZN7testing12_GLOBAL__N_124PrintBytesInObjectToImplEPKhmPSo
-   fun:_ZN7testing9internal220PrintBytesInObjectToEPKhmPSo
-   fun:_ZN7testing9internal220TypeWithoutFormatterI18DownloadCreateInfoLNS0_8TypeKindE2EE10PrintValueERKS2_PSo
-   fun:_ZN7testing9internal2lsIcSt11char_traitsIcE18DownloadCreateInfoEERSt13basic_ostreamIT_T0_ES9_RKT1_
-   fun:_ZN16testing_internal26DefaultPrintNonContainerToI18DownloadCreateInfoEEvRKT_PSo
-   fun:_ZN7testing8internal14DefaultPrintToI18DownloadCreateInfoEEvcNS0_13bool_constantILb0EEERKT_PSo
-   fun:_ZN7testing8internal7PrintToI18DownloadCreateInfoEEvRKT_PSo
-   fun:_ZN7testing8internal16UniversalPrinterI18DownloadCreateInfoE5PrintERKS2_PSo
-   fun:_ZN7testing8internal14UniversalPrintI18DownloadCreateInfoEEvRKT_PSo
-   fun:_ZN7testing8internal20MatchPrintAndExplainI18DownloadCreateInfoRKS2_EEbRT_RKNS_7MatcherIT0_EEPNS_19MatchResultListenerE
-}