Add trial for DirectWrite, and reorder some initialization so it can take effect

content/common/sandbox_win.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/common/sandbox_win.h"
 
 #include <string>
 
 #include "base/base_switches.h"
 #include "base/command_line.h"
 #include "base/debug/profiler.h"
 #include "base/debug/trace_event.h"
 #include "base/file_util.h"
 #include "base/hash.h"
+#include "base/metrics/field_trial.h"
 #include "base/path_service.h"
 #include "base/process/launch.h"
 #include "base/strings/string_util.h"
 #include "base/strings/stringprintf.h"
 #include "base/win/iat_patch_function.h"
 #include "base/win/scoped_handle.h"
 #include "base/win/scoped_process_information.h"
 #include "base/win/windows_version.h"
 #include "content/public/common/content_client.h"
 #include "content/public/common/content_switches.h"
 #include "content/public/common/sandbox_init.h"
 #include "content/public/common/sandboxed_process_launcher_delegate.h"
 #include "sandbox/win/src/process_mitigations.h"
 #include "sandbox/win/src/sandbox.h"
 #include "sandbox/win/src/sandbox_nt_util.h"
 #include "sandbox/win/src/win_utils.h"
+#include "ui/gfx/win/dpi.h"
 
 static sandbox::BrokerServices* g_broker_services = NULL;
 static sandbox::TargetServices* g_target_services = NULL;
 
 namespace content {
 namespace {
 
 // The DLLs listed here are known (or under strong suspicion) of causing crashes
 // when they are loaded in the renderer. Note: at runtime we generate short
 // versions of the dll name only if the dll has an extension.
@@ skipping 518 matching lines @@
   sandbox::ResultCode result = target_services->Init();
   g_target_services = target_services;
   return sandbox::SBOX_ALL_OK == result;
 }
 
 bool ShouldUseDirectWrite() {
   // If the flag is currently on, and we're on Win7 or above, we enable
   // DirectWrite. Skia does not require the additions to DirectWrite in QFE
   // 2670838, so a Win7 check is sufficient. We do not currently attempt to
   // support Vista, where SP2 and the Platform Update are required.
+  if (base::win::GetVersion() < base::win::VERSION_WIN7)
+    return false;
+
+  // If forced off, don't use it.
   const CommandLine& command_line = *CommandLine::ForCurrentProcess();
-  return !command_line.HasSwitch(switches::kDisableDirectWrite) &&
-         base::win::GetVersion() >= base::win::VERSION_WIN7;
+  if (command_line.HasSwitch(switches::kDisableDirectWrite))

[Alexei Svitkine (slow), 2014/06/17 21:30:29]

Do you want to see data from users who've manually toggled their flags as
separate groups on the dashboard? If so, you can follow the pattern suggested at
go/finch-and-flags to get that effect. If you don't care, then feel free to
ignore as this will be fine otherwise.

But it might be a good signal to see if people are manually disabling the
experimental group.

(If you do follow that suggested pattern, you should probably put the DPI scale
check above this, just below the version check.)

[scottmg, 2014/06/17 22:07:00]

Thanks, I think we don't care too much as there's many reasons (aesthetic,
preference, etc.) that people might force it off.

+    return false;
+
+  // Can't use GDI on HiDPI.
+  if (gfx::GetDPIScale() > 1.0f)
+    return true;
+
+  // Otherwise, Finch.
+  const std::string group_name =
+      base::FieldTrialList::FindFullName("DirectWrite");
+  return group_name != "Disabled";

[Alexei Svitkine (slow), 2014/06/17 21:30:29]

Instead of checking for != "Disabled", check for "Enabled" instead. That way,
you can have a group called "Control" that exercises the default behavior.

[Alexei Svitkine (slow), 2014/06/17 22:02:15]

Sorry, I just read your experiment description and you want the default to be
enabled, so the above makes sense now. Please ignore this comment.

[scottmg, 2014/06/17 22:07:00]

Done.

[scottmg, 2014/06/17 22:07:00]

Yeah, ok thanks. Seems like it'd work either way, depending on the server-side.
I'm still working through that CL.

 }
 
 base::ProcessHandle StartSandboxedProcess(
     SandboxedProcessLauncherDelegate* delegate,
     CommandLine* cmd_line) {
   const CommandLine& browser_command_line = *CommandLine::ForCurrentProcess();
   std::string type_str = cmd_line->GetSwitchValueASCII(switches::kProcessType);
 
   TRACE_EVENT_BEGIN_ETW("StartProcessWithAccess", 0, type_str);
 
@@ skipping 167 matching lines @@
   }
 
   return false;
 }
 
 bool BrokerAddTargetPeer(HANDLE peer_process) {
   return g_broker_services->AddTargetPeer(peer_process) == sandbox::SBOX_ALL_OK;
 }
 
 }  // namespace content