Move vertex buffer setup out of drawPackedGlyph().

This gets a very welcome ~10% speedup on my Mac.

Committed: https://skia.googlesource.com/skia/+/1d38619389cc1100bd516b9acbf17b7bd42d33ce

R=bsalomon@google.com

Author: jvanverth@google.com

Review URL: https://codereview.chromium.org/414573002
diff --git a/src/gpu/GrDistanceFieldTextContext.h b/src/gpu/GrDistanceFieldTextContext.h
index 3a602f0..7676fc1 100644
--- a/src/gpu/GrDistanceFieldTextContext.h
+++ b/src/gpu/GrDistanceFieldTextContext.h
@@ -48,9 +48,7 @@
         kDefaultRequestedVerts   = kDefaultRequestedGlyphs * 4,
     };
 
-    SkPoint*                fVertices;
-    int32_t                 fMaxVertices;
-    GrTexture*              fCurrTexture;
+    void*                   fVertices;
     int                     fCurrVertex;
 };