Initial implementation for sharing field trial state (win)

content/browser/gpu/gpu_process_host.cc

Index: content/browser/gpu/gpu_process_host.cc
diff --git a/content/browser/gpu/gpu_process_host.cc b/content/browser/gpu/gpu_process_host.cc
index 367a69d9323fd065203a78416690ba86d09ad846..23e756a50b0948bd557738e31629e7f678596019 100644
--- a/content/browser/gpu/gpu_process_host.cc
+++ b/content/browser/gpu/gpu_process_host.cc
@@ -48,6 +48,7 @@
 #include "content/public/browser/render_widget_host_view_frame_subscriber.h"
 #include "content/public/common/connection_filter.h"
 #include "content/public/common/content_client.h"
+#include "content/public/common/content_features.h"
 #include "content/public/common/content_switches.h"
 #include "content/public/common/mojo_channel_switches.h"
 #include "content/public/common/mojo_shell_connection.h"
@@ -973,8 +974,20 @@ bool GpuProcessHost::LaunchGpuProcess(gpu::GpuPreferences* gpu_preferences) {
 
   base::CommandLine* cmd_line = new base::CommandLine(exe_path);
 #endif
+
   cmd_line->AppendSwitchASCII(switches::kProcessType, switches::kGpuProcess);
-  BrowserChildProcessHostImpl::CopyFeatureAndFieldTrialFlags(cmd_line);
+
+#if defined(OS_WIN)
+  if (base::FeatureList::IsEnabled(
+          features::kShareFieldTrialStateViaSharedMemory))

[Alexei Svitkine (slow), 2016/10/04 18:49:35]

Nit: {}'s

[lawrencewu, 2016/10/05 20:57:56]

Done.

+    field_trial_state_.reset(new base::SharedMemory());
+#endif
+  BrowserChildProcessHostImpl::CopyFeatureAndFieldTrialFlags(
+      cmd_line, field_trial_state_.get());
+#if defined(OS_WIN)
+  if (!field_trial_state_.get()->handle().GetHandle())

[Alexei Svitkine (slow), 2016/10/04 18:49:36]

Is this just an error case? Needs a comment at the very least.

[lawrencewu, 2016/10/05 20:57:56]

Yes, it is the case when there were no field trials (happens in browsertests).
The handle will still try to get passed down but won't work because it's
invalid. With the new changes we don't need to do this anymore, it's implicit in
the flow.

+    field_trial_state_.reset();
+#endif
 
 #if defined(OS_WIN)
   cmd_line->AppendArg(switches::kPrefetchArgumentGpu);
@@ -1018,10 +1031,8 @@ bool GpuProcessHost::LaunchGpuProcess(gpu::GpuPreferences* gpu_preferences) {
     cmd_line->PrependWrapper(gpu_launcher);
 
   process_->Launch(
-      new GpuSandboxedProcessLauncherDelegate(cmd_line,
-                                              process_->GetHost()),
-      cmd_line,
-      true);
+      new GpuSandboxedProcessLauncherDelegate(cmd_line, process_->GetHost()),
+      cmd_line, field_trial_state_.get(), true);
   process_launched_ = true;
 
   UMA_HISTOGRAM_ENUMERATION("GPU.GPUProcessLifetimeEvents",