[Webrtc] Reenable libc++ on ubsan

tools_webrtc/ubsan/vptr_blacklist.txt

Index: tools_webrtc/ubsan/vptr_blacklist.txt
diff --git a/tools_webrtc/ubsan/vptr_blacklist.txt b/tools_webrtc/ubsan/vptr_blacklist.txt
index 02adc84630cd46b4c1578d3590791a62d0969f49..739de3665928dcc791732237fc164c52d48897c9 100644
--- a/tools_webrtc/ubsan/vptr_blacklist.txt
+++ b/tools_webrtc/ubsan/vptr_blacklist.txt
@@ -20,3 +20,8 @@ src:*/third_party/protobuf/src/google/protobuf/compiler/plugin.pb.cc
 src:*/third_party/protobuf/src/google/protobuf/compiler/cpp/cpp_message.cc
 src:*/third_party/protobuf/src/google/protobuf/descriptor.pb.cc
 
+#############################################################################
+# UBsan goes into an infinite recursion when __dynamic_cast instrumented with
+# "vptr". See crbug.com/609786.
+
+src:*/third_party/libc\+\+abi/trunk/src/private_typeinfo.cpp