Add finch control for use-zoom-for-dsf.

content/common/content_switches_internal.cc

 // Copyright (c) 2014 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/content_switches_internal.h"
 
 #include <string>
 
 #include "base/command_line.h"
+#include "base/feature_list.h"
 #include "base/metrics/field_trial.h"
 #include "build/build_config.h"
 #include "content/public/common/content_switches.h"
 
 #if defined(OS_WIN)
 #include "base/win/windows_version.h"
 #endif
 
 namespace content {
 
 namespace {
 
+const base::Feature kUseZoomForDsfEnabledByDefault {

[Will Harris, 2016/07/14 22:42:56]

I use constexpr here but I think it's the same difference.

[Bret, 2016/07/15 18:14:28]

The example used const and this seems to work fine so I think I'll leave it.

+  "use-zoom-for-dsf enabled by default", base::FEATURE_ENABLED_BY_DEFAULT
+};
+
 bool IsUseZoomForDSFEnabledByDefault() {
-#if defined(OS_CHROMEOS) || defined(OS_WIN)
+#if defined(OS_CHROMEOS)
   return true;
+#elif defined(OS_WIN)
+  return base::FeatureList::IsEnabled(kUseZoomForDsfEnabledByDefault);
 #else
   return false;
 #endif
 }
 
 }  // namespace
 
 bool IsPinchToZoomEnabled() {
   const base::CommandLine& command_line =
       *base::CommandLine::ForCurrentProcess();
@@ skipping 60 matching lines @@
     return ProgressBarCompletion::DOM_CONTENT_LOADED;
   if (progress_bar_completion ==
       "resourcesBeforeDOMContentLoadedAndSameOriginIframes") {
     return ProgressBarCompletion::RESOURCES_BEFORE_DCL_AND_SAME_ORIGIN_IFRAMES;
   }
 #endif
   return ProgressBarCompletion::LOAD_EVENT;
 }
 
 } // namespace content