Use SkLazyPtr in SkPDFGraphicState.cpp

Motivation: currently we rely on mutexes for guarding static
initialization.  These mutexes will go away.

Review URL: https://codereview.chromium.org/815223005
diff --git a/src/pdf/SkPDFGraphicState.h b/src/pdf/SkPDFGraphicState.h
index cfc80ff..1c54e6c 100644
--- a/src/pdf/SkPDFGraphicState.h
+++ b/src/pdf/SkPDFGraphicState.h
@@ -73,6 +73,9 @@
 
     bool equals(const SkPaint&) const;
 
+    // Only public for SK_DECLARE_STATIC_LAZY_PTR
+    static SkPDFGraphicState* CreateNoSMaskGraphicState();
+
 private:
     const SkPaint fPaint;
     SkTDArray<SkPDFObject*> fResources;