Add logic to switch to DirectWrite font proxy via field trial.

content/common/dwrite_font_platform_win.cc

 // Copyright 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/public/common/dwrite_font_platform_win.h"
 
+#include <dwrite.h>
 #include <windows.h>
+#include <wrl/implements.h>
+#include <wrl/wrappers/corewrappers.h>
+
 #include <stddef.h>
 #include <stdint.h>
 
-#include <dwrite.h>
-#include <wrl/implements.h>
-#include <wrl/wrappers/corewrappers.h>
-
 #include <limits>
 #include <map>
 #include <string>
 #include <utility>
 #include <vector>
 
 #include "base/command_line.h"
 #include "base/debug/alias.h"
 #include "base/debug/crash_logging.h"
 #include "base/files/file_enumerator.h"
@@ skipping 1241 matching lines @@
   DCHECK(!g_shared_font_cache.IsValid());
   g_shared_font_cache.Set(mapping);
 
   return true;
 }
 
 bool BuildFontCache(const base::FilePath& file) {
   return BuildFontCacheInternal(file.value().c_str());
 }
 
+bool ShouldUseDirectWriteFontProxyFieldTrial() {
+  return base::StartsWith(
+      base::FieldTrialList::FindFullName("DirectWriteFontProxy"),
+      "UseDirectWriteFontProxy", base::CompareCase::SENSITIVE);
+}
+
 }  // namespace content