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

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 f9825fef0c734f36243cd7be4259db2e596b8a1f..f7025ef0d4a7da330d4f8f9ac3056630720fe960 100644
--- a/content/common/font_warmup_win.cc
+++ b/content/common/font_warmup_win.cc
@@ -23,6 +23,7 @@
 #include "base/win/iat_patch_function.h"
 #include "base/win/windows_version.h"
 #include "content/public/common/dwrite_font_platform_win.h"
+#include "ppapi/shared_impl/proxy_lock.h"
 #include "skia/ext/fontmgr_default_win.h"
 #include "skia/ext/refptr.h"
 #include "third_party/WebKit/public/web/win/WebFontRendering.h"
@@ -255,6 +256,7 @@ skia::RefPtr<SkTypeface> GetTypefaceFromLOGFONT(const LOGFONTW* log_font) {
                                        : SkFontStyle::kUpright_Slant);
 
   std::string family_name = base::WideToUTF8(log_font->lfFaceName);
+  ppapi::ProxyAutoLock lock;  // Needed for DirectWrite font proxy.
   return skia::AdoptRef(
       g_warmup_fontmgr->matchFamilyStyle(family_name.c_str(), style));
 }
@@ -486,7 +488,10 @@ SkFontMgr* GetPreSandboxWarmupFontMgr() {
 }
 
 GdiFontPatchData* PatchGdiFontEnumeration(const base::FilePath& path) {
-  // We assume the fontmgr is already warmed up before calling this.
+  if (content::ShouldUseDirectWriteFontProxyFieldTrial() && !g_warmup_fontmgr)
+    g_warmup_fontmgr = SkFontMgr_New_DirectWrite();

[fdoray, 2015/12/31 03:18:16]

Is this object leaked during shutdown? If we want to leak the object, can we say
it explicitly in a comment? Otherwise, should we use a
base::LazyInstance<skia::RefPtr<SkFontMgr>>?

[Ilya Kulshin, 2016/01/08 00:44:23]

The previous code was leaking it, I guess I hadn't thought of it as a concern
(it's just a single object that otherwise lives for the duration of the process
anyway). LazyInstance<RefPtr> runs into problems with lifetime and destruction,
so I added a comment.

+  // If not using the font proxy, we assume |g_warmup_fontmgr| is already
+  // initialized before this function is called.
   DCHECK(g_warmup_fontmgr);
   return new GdiFontPatchDataImpl(path);
 }