Use RecvMsgWithPid to find real PID for zygote children

content/zygote/zygote_linux.h

Index: content/zygote/zygote_linux.h
diff --git a/content/zygote/zygote_linux.h b/content/zygote/zygote_linux.h
index 4aa2f03d3bfbf8b2bc23706d5d53ec3b37b7db6f..fd20f60fab866f463959f9efcc324afefefb9e63 100644
--- a/content/zygote/zygote_linux.h
+++ b/content/zygote/zygote_linux.h
@@ -81,6 +81,7 @@ class Zygote {
   int ForkWithRealPid(const std::string& process_type,
                       const base::GlobalDescriptors::Mapping& fd_mapping,
                       const std::string& channel_id,
+                      base::ScopedFD pid_oracle,
                       std::string* uma_name,
                       int* uma_sample,
                       int* uma_boundary_value);