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 dec1c16b3c5d2787692ab18af00c38041d8f2844..56140f421aae388d5eb07c3b4eaf3ec0639dbf04 100644
--- a/content/common/dwrite_font_platform_win.cc
+++ b/content/common/dwrite_font_platform_win.cc
@@ -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