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

content/common/dwrite_font_platform_win.cc

Index: content/common/dwrite_font_platform_win.cc
diff --git a/content/common/dwrite_font_platform_win.cc b/content/common/dwrite_font_platform_win.cc
index 25755f5847b5bb372cece0c4b10cd0841a81951f..2cc8749ceb436c64023fac218b2b242c143b78b9 100644
--- a/content/common/dwrite_font_platform_win.cc
+++ b/content/common/dwrite_font_platform_win.cc
@@ -4,14 +4,14 @@
 
 #include "content/public/common/dwrite_font_platform_win.h"
 
-#include <windows.h>
-#include <stddef.h>
-#include <stdint.h>
-
 #include <dwrite.h>
+#include <windows.h>
 #include <wrl/implements.h>
 #include <wrl/wrappers/corewrappers.h>
 
+#include <stddef.h>
+#include <stdint.h>
+
 #include <limits>
 #include <map>
 #include <string>
@@ -1273,4 +1273,10 @@ 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