Share field trial allocator on zygote-using Linuxes

content/app/content_main_runner.cc

Index: content/app/content_main_runner.cc
diff --git a/content/app/content_main_runner.cc b/content/app/content_main_runner.cc
index 9d92e28e19c5d1133b7af61925cf10f53b04fe4d..135fe21718ec6c733bef117f2384644ead160b7c 100644
--- a/content/app/content_main_runner.cc
+++ b/content/app/content_main_runner.cc
@@ -144,8 +144,20 @@ void InitializeFieldTrialAndFeatureList(
 
   // Ensure any field trials in browser are reflected into the child
   // process.
+#if defined(OS_POSIX) && !defined(OS_NACL) && !defined(OS_MACOSX) && \
+    !defined(OS_ANDROID)
+  // On POSIX systems that use the zygote, we get the trials from a shared
+  // memory segment backed by an fd instead of the command line.
+  bool result =
+      base::FieldTrialList::CreateTrialsFromDescriptor(kFieldTrialDescriptor);
+  if (!result) {
+    base::FieldTrialList::CreateTrialsFromCommandLine(
+        command_line, switches::kFieldTrialHandle);
+  }

[Alexei Svitkine (slow), 2016/11/29 17:38:27]

I actually prefer you previous version which keeps the fall back logic within
the field trial code rather than leaking it here.

I think it's fine to add the extra param and you can just document on which
platforms each is used.

[lawrencewu, 2016/11/29 19:11:20]

Done.

+#else
   base::FieldTrialList::CreateTrialsFromCommandLine(
       command_line, switches::kFieldTrialHandle);
+#endif
 
   std::unique_ptr<base::FeatureList> feature_list(new base::FeatureList);
   feature_list->InitializeFromCommandLine(
@@ -478,6 +490,10 @@ class ContentMainRunnerImpl : public ContentMainRunner {
     SetupSignalHandlers();
     g_fds->Set(kMojoIPCChannel,
                kMojoIPCChannel + base::GlobalDescriptors::kBaseDescriptor);
+
+    g_fds->Set(
+        kFieldTrialDescriptor,
+        kFieldTrialDescriptor + base::GlobalDescriptors::kBaseDescriptor);
 #endif  // !OS_ANDROID
 
 #if defined(OS_LINUX) || defined(OS_OPENBSD)