Add CPU backing store for GrAtlas to reduce texture uploads

src/gpu/GrBitmapTextContext.h

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef GrBitmapTextContext_DEFINED
 #define GrBitmapTextContext_DEFINED
 
 #include "GrTextContext.h"
 
 class GrTextStrike;
+class GrAtlasMgr;
 
 /*
  * This class implements GrTextContext using standard bitmap fonts
  */
 class GrBitmapTextContext : public GrTextContext {
 public:
     GrBitmapTextContext(GrContext*, const SkDeviceProperties&);
     virtual ~GrBitmapTextContext();
 
     virtual void drawText(const GrPaint&, const SkPaint&, const char text[], size_t byteLength,
@@ skipping 21 matching lines @@
     };
 
     SkPoint*                fVertices;
     int32_t                 fMaxVertices;
     GrTexture*              fCurrTexture;
     int                     fCurrVertex;
     SkRect                  fVertexBounds;
 };
 
 #endif