Add suppressions for memcheck errors.

tools/valgrind-webrtc/memcheck/suppressions.txt

 # This file is used in addition to the one already maintained in Chrome.
 # It acts as a place holder for future additions for WebRTC.
 # It must exist for the Python wrapper script to work properly.
 
 # There are three kinds of suppressions in this file.
 # 1. third_party libraries
 # 2. webrtc stuff
 # 3. libjingle stuff (talk folder)
 #-----------------------------------------------------------------------
 
@@ skipping 423 matching lines @@
    Memcheck:Uninitialized
    fun:_ZN6webrtc11DataChannel4InitERKNS_23InternalDataChannelInitE
    ...
 }
 {
    bug_5984
    Memcheck:Uninitialized
    fun:_ZN6webrtc15GainControlImpl19ProcessCaptureAudioEPNS_11AudioBufferEb
    ...
 }
+{
+   bug_5986
+   Memcheck:Unaddressable
+   fun:silk_stereo_LR_to_MS
+   fun:silk_Encode
+   fun:opus_encode_native
+   ...
+}
+{
+   bug_5987
+   Memcheck:Leak
+   fun:_Znw*
+   fun:_ZN6webrtc51AudioEncoderCopyRedDeathTest_NullSpeechEncoder_Test8TestBodyEv
+}
+{
+   bug_5988
+   Memcheck:Leak
+   fun:_Znw*
+   fun:_ZNSt8_Rb_treeISsSt4pairIKSsSsESt10_Select1stIS2_EN3rtc5ilessESaIS2_EE15_M_insert_equalIS2_EESt17_Rb_tree_iteratorIS2_EOT_
+   fun:_ZN3rtc8HttpData12changeHeaderERKSsS2_NS0_13HeaderCombineE
+   fun:_ZN3rtc16HttpResponseData9set_errorEj
+   fun:_ZN3rtc12_GLOBAL__N_117HttpServerMonitor9OnRequestEPNS_10HttpServerEPNS_21HttpServerTransactionE
+   fun:_ZN3rtc10HttpServer10Connection14onHttpCompleteENS_8HttpModeENS_9HttpErrorE
+   fun:_ZN3rtc8HttpBase10OnCompleteENS_9HttpErrorE
+   fun:_ZN3rtc8HttpBase17OnHttpStreamEventEPNS_15StreamInterfaceEii
+   fun:_ZN7testing12StreamSource11QueueStringEPKc
+   fun:_ZN3rtc12_GLOBAL__N_122CreateClientConnectionERNS_10HttpServerERNS0_17HttpServerMonitorEb
+   fun:_ZN3rtc47HttpServer_SignalsCloseAfterForcedCloseAll_Test8TestBodyEv
+}
+{
+   bug_5989
+   Memcheck:Unaddressable
+   ...
+   fun:_ZNK3rtc15CriticalSection5EnterEv
+   ...
+}