Use RecvMsgWithPid to find real PID for zygote children

content/common/child_process_sandbox_support_impl_linux.cc

Index: content/common/child_process_sandbox_support_impl_linux.cc
diff --git a/content/common/child_process_sandbox_support_impl_linux.cc b/content/common/child_process_sandbox_support_impl_linux.cc
index a810e5c42c005f2bb600ca27af2763ec7c3ebe25..c0edcfcf40a2a9ffe5bda4d2570129fbc6b0ee93 100644
--- a/content/common/child_process_sandbox_support_impl_linux.cc
+++ b/content/common/child_process_sandbox_support_impl_linux.cc
@@ -14,6 +14,7 @@
 #include "base/posix/unix_domain_socket_linux.h"
 #include "base/sys_byteorder.h"
 #include "content/common/sandbox_linux/sandbox_linux.h"
+#include "content/common/zygote_commands_linux.h"
 #include "third_party/WebKit/public/platform/linux/WebFontFamily.h"
 #include "third_party/WebKit/public/platform/linux/WebFontRenderStyle.h"
 
@@ -181,4 +182,11 @@ bool GetFontTable(int fd, uint32_t table_tag, off_t offset,
   return true;
 }
 
+bool SendZygoteChildPing(int fd) {
+  return UnixDomainSocket::SendMsg(fd,
+                                   kZygoteChildPingMessage,
+                                   sizeof(kZygoteChildPingMessage),
+                                   std::vector<int>());
+}
+
 }  // namespace content