SkPDF: Add Sfntly to DEPS, gyp

Note: this can be disabled via:
    GYP_DEFINES='skia_pdf_use_sfntly=0

Warning: dm is 34% slower and uses 9% more memory.  This is
okay.

Motivation: We want to test this code path in DM, since it is
always used by Chromium and Android.

BUG=skia:3563

Committed: https://skia.googlesource.com/skia/+/6a53b04e26749ea61f690ece408f2a1c0a5ad5bb

Review URL: https://codereview.chromium.org/1134683006
diff --git a/src/pdf/SkPDFFont.cpp b/src/pdf/SkPDFFont.cpp
index 0afdb9b..e531df0 100644
--- a/src/pdf/SkPDFFont.cpp
+++ b/src/pdf/SkPDFFont.cpp
@@ -24,14 +24,12 @@
 #include "SkTypes.h"
 #include "SkUtils.h"
 
-#if defined (SK_SFNTLY_SUBSETTER)
-    #include SK_SFNTLY_SUBSETTER
-#endif
-
 #if defined (GOOGLE3)
     // #including #defines doesn't work in with this build system.
     #include "typography/font/sfntly/src/sample/chromium/font_subsetter.h"
     #define SK_SFNTLY_SUBSETTER  // For the benefit of #ifdefs below.
+#elif defined (SK_SFNTLY_SUBSETTER)
+    #include SK_SFNTLY_SUBSETTER
 #endif
 
 // PDF's notion of symbolic vs non-symbolic is related to the character set, not