Dont try to draw glyphs with unexpected mask formats

src/gpu/GrBatchFontCache.h

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef GrBatchFontCache_DEFINED
 #define GrBatchFontCache_DEFINED
 
@@ skipping 22 matching lines @@
 
     inline GrGlyph* getGlyph(const SkGlyph& skGlyph, GrGlyph::PackedID packed,
                              GrFontScaler* scaler) {
         GrGlyph* glyph = fCache.find(packed);
         if (NULL == glyph) {
             glyph = this->generateGlyph(skGlyph, packed, scaler);
         }
         return glyph;
     }
 
-    // returns true if glyph successfully added to texture atlas, false otherwise
-    bool addGlyphToAtlas(GrBatchTarget*, GrGlyph*, GrFontScaler*, const SkGlyph&);
+    // returns true if glyph successfully added to texture atlas, false otherwise.  If the glyph's
+    // mask format has changed, then addGlyphToAtlas will draw a clear box.  This will almost never
+    // happen.
+    // TODO we can handle some of these cases if we really want to, but the long term solution is to
+    // get the actual glyph image itself when we get the glyph metrics.
+    bool addGlyphToAtlas(GrBatchTarget*, GrGlyph*, GrFontScaler*, const SkGlyph&,
+                         GrMaskFormat expectedMaskFormat);
 
     // testing
     int countGlyphs() const { return fCache.count(); }
 
     // remove any references to this plot
     void removeID(GrBatchAtlas::AtlasID);
 
     // If a TextStrike is abandoned by the cache, then the caller must get a new strike
     bool isAbandoned() const { return fIsAbandoned; }
 
@@ skipping 136 matching lines @@
 
     static void HandleEviction(GrBatchAtlas::AtlasID, void*);
 
     GrContext* fContext;
     SkTDynamicHash<GrBatchTextStrike, GrFontDescKey> fCache;
     GrBatchAtlas* fAtlases[kMaskFormatCount];
     GrBatchTextStrike* fPreserveStrike;
 };
 
 #endif