Suppress uninitialized read report in WebRtcAudioRenderer::SourceCallback on MacOS

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 # running overnight and removing outdated bugs/suppressions.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 2352 matching lines @@
    fun:_ZN5media19ScreenCaptureDevice4Core7DoStartEv
 }
 {
    bug_244420
    Memcheck:Uninitialized
    ...
    fun:_ZN9talk_baseL8ToStringIyEESsRKT_
    fun:_ZN7content23VideoDestinationHandler4OpenEPNS_28MediaStreamDependencyFactoryEPNS_28MediaStreamRegistryInterfaceERKSsPPNS_20FrameWriterInterfaceE
    fun:_ZN7content37VideoDestinationHandlerTest_Open_Test8TestBodyEv
 }
+{
+   bug_244437
+   Memcheck:Uninitialized
+   fun:_ZN5mediaL23FromInterleavedInternalIssLs0EEEvPKviiPNS_8AudioBusEff
+   fun:_ZN5media8AudioBus22FromInterleavedPartialEPKviii
+   fun:_ZN5media8AudioBus15FromInterleavedEPKvii
+   fun:_ZN7content19WebRtcAudioRenderer14SourceCallbackEiPN5media8AudioBusE
+}