Move ForkWithFlags from sandbox/ to base/ and plug it into LaunchProcess.

content/zygote/zygote_linux.cc

Index: content/zygote/zygote_linux.cc
diff --git a/content/zygote/zygote_linux.cc b/content/zygote/zygote_linux.cc
index 051f791088d36ed295aa5f070ef58829e7aef0cd..ba2097ae277f921ec1eae356b211a8b2ec594b08 100644
--- a/content/zygote/zygote_linux.cc
+++ b/content/zygote/zygote_linux.cc
@@ -374,7 +374,7 @@ int Zygote::ForkWithRealPid(const std::string& process_type,
     CreatePipe(&read_pipe, &write_pipe);
     // This is roughly equivalent to a fork(). We are using ForkWithFlags mainly
     // to give it some more diverse test coverage.
-    pid = sandbox::ForkWithFlags(SIGCHLD, nullptr, nullptr);
+    pid = base::ForkWithFlags(SIGCHLD, nullptr, nullptr);
   }
 
   if (pid == 0) {