Fix thread unsafe mutex initialization.

BUG=skia:2779
R=robertphillips@google.com, mtklein@google.com, reed@android.com, bsalomon@google.com

Author: bungeman@google.com

Review URL: https://codereview.chromium.org/419113002
diff --git a/include/gpu/GrFontScaler.h b/include/gpu/GrFontScaler.h
index d90708d..0376038 100644
--- a/include/gpu/GrFontScaler.h
+++ b/include/gpu/GrFontScaler.h
@@ -21,7 +21,7 @@
  */
 class GrFontDescKey : public SkRefCnt {
 public:
-    SK_DECLARE_INST_COUNT(SkGrDescKey)
+    SK_DECLARE_INST_COUNT(GrFontDescKey)
     
     typedef uint32_t Hash;