Suppress Memcheck:Uninitialized error when printing rtc::optional.

tools-webrtc/valgrind/memcheck/suppressions.txt

Index: tools-webrtc/valgrind/memcheck/suppressions.txt
diff --git a/tools-webrtc/valgrind/memcheck/suppressions.txt b/tools-webrtc/valgrind/memcheck/suppressions.txt
index bfb8ffcb88a3974f5405ce9c76250fc6c7fdb164..6182f56d7061c447ce92bd3b2122c38a6f4900a8 100644
--- a/tools-webrtc/valgrind/memcheck/suppressions.txt
+++ b/tools-webrtc/valgrind/memcheck/suppressions.txt
@@ -530,3 +530,15 @@
    fun:WebRtcOpus_Decode*
    ...
 }
+{
+   bug_687087
+   Memcheck:Uninitialized
+   fun:vfprintf
+   fun:vsnprintf
+   fun:snprintf
+   fun:_ZN7testing12_GLOBAL__N_126PrintByteSegmentInObjectToEPKhmmPSo
+   fun:_ZN7testing9internal220PrintBytesInObjectToEPKhmPSo
+   fun:_ZN7testing8internal25UntypedFunctionMockerBase17UntypedInvokeWithEPKv
+   fun:_ZNK6webrtc11MockRtpRtcp11FlexfecSsrcEv
+   ...
+}