Add plumbing in blink to allow overriding the default font collection.

content/common/font_warmup_win.cc

Index: content/common/font_warmup_win.cc
diff --git a/content/common/font_warmup_win.cc b/content/common/font_warmup_win.cc
index 2968218c231a88281bdca074aa94eafc8bb30dbe..fe1c0a0dd192a0f1f4c843265a59a0eea9aba132 100644
--- a/content/common/font_warmup_win.cc
+++ b/content/common/font_warmup_win.cc
@@ -482,8 +482,8 @@ SkFontMgr* GetPreSandboxWarmupFontMgr() {
 
     PatchDWriteFactory(factory);
 
-    blink::WebFontRendering::setDirectWriteFactory(factory);
     g_warmup_fontmgr = SkFontMgr_New_DirectWrite(factory);
+    blink::WebFontRendering::setSkiaFontManager(g_warmup_fontmgr);
   }
   return g_warmup_fontmgr;
 }