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

content/common/content_switches_internal.cc

Index: content/common/content_switches_internal.cc
diff --git a/content/common/content_switches_internal.cc b/content/common/content_switches_internal.cc
index fa7ab4baafd8a5f035f28d025541c635af4dbb6c..f7eb5764e3ddf0b7908d3fceaa1b4d0feace3e76 100644
--- a/content/common/content_switches_internal.cc
+++ b/content/common/content_switches_internal.cc
@@ -7,6 +7,7 @@
 #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"
@@ -19,9 +20,15 @@ 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