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

You can set --force-fieldtrials="DirectWrite/Disabled/" to turn DirectWrite off.

R=cpu@chromium.org, jamesr@chromium.org, asvitkine@chromium.org
BUG=385778

Review URL: https://codereview.chromium.org/335223003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@278238 0039d316-1c4b-4281-b951-d872f2087c98

content/common/sandbox_win.cc

@@ -12,6 +12,7 @@
 #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"
@@ -28,6 +29,7 @@
 #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;
@@ -566,9 +568,24 @@ bool ShouldUseDirectWrite() {
   // 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))
+    return false;
+
+#if !defined(NACL_WIN64)
+  // Can't use GDI on HiDPI.
+  if (gfx::GetDPIScale() > 1.0f)
+    return true;
+#endif
+
+  // Otherwise, check the field trial.
+  const std::string group_name =
+      base::FieldTrialList::FindFullName("DirectWrite");
+  return group_name != "Disabled";
 }
 
 base::ProcessHandle StartSandboxedProcess(

content/renderer/renderer_main.cc

@@ -178,8 +178,6 @@ int RendererMain(const MainFunctionParams& parameters) {
 
   base::PlatformThread::SetName("CrRendererMain");
 
-  platform.PlatformInitialize();
-
   bool no_sandbox = parsed_command_line.HasSwitch(switches::kNoSandbox);
 
   // Initialize histogram statistics gathering system.
@@ -200,6 +198,9 @@ int RendererMain(const MainFunctionParams& parameters) {
     DCHECK(result);
   }
 
+  // PlatformInitialize uses FieldTrials, so this must happen later.
+  platform.PlatformInitialize();
+
 #if defined(ENABLE_PLUGINS)
   // Load pepper plugins before engaging the sandbox.
   PepperPluginRegistry::GetInstance();