remove unused (by the outside) SkImage::newSurface, and simplify newImage -> newSubset

src/image/SkImage_Gpu.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 SkImage_Gpu_DEFINED
 #define SkImage_Gpu_DEFINED
 
 #include "SkAtomics.h"
 #include "GrTexture.h"
 #include "GrGpuResourcePriv.h"
 #include "SkBitmap.h"
 #include "SkImage_Base.h"
 #include "SkImagePriv.h"
 #include "SkSurface.h"
 
 class SkImage_Gpu : public SkImage_Base {
 public:
     /**
      *  An "image" can be a subset/window into a larger texture, so we explicit take the
      *  width and height.
      */
-    SkImage_Gpu(int w, int h, uint32_t uniqueID, SkAlphaType, GrTexture*,
-                int sampleCountForNewSurfaces, SkSurface::Budgeted);
+    SkImage_Gpu(int w, int h, uint32_t uniqueID, SkAlphaType, GrTexture*, SkSurface::Budgeted);
     ~SkImage_Gpu() override;
 
     void applyBudgetDecision() const {
         GrTexture* tex = this->getTexture();
         SkASSERT(tex);
         if (fBudgeted) {
             tex->resourcePriv().makeBudgeted();
         } else {
             tex->resourcePriv().makeUnbudgeted();
         }
     }
 
     bool getROPixels(SkBitmap*) const override;
     GrTexture* asTextureRef(GrContext* ctx, SkImageUsageType usage) const override;
+    SkImage* onNewSubset(const SkIRect&) const override;
 
     GrTexture* peekTexture() const override { return fTexture; }
     SkShader* onNewShader(SkShader::TileMode,
                           SkShader::TileMode,
                           const SkMatrix* localMatrix) const override;
     bool isOpaque() const override;
-    SkSurface* onNewSurface(const SkImageInfo&, const SkSurfaceProps&) const override;
     bool onReadPixels(const SkImageInfo&, void* dstPixels, size_t dstRowBytes,
                       int srcX, int srcY) const override;
 
 private:
     SkAutoTUnref<GrTexture>     fTexture;
-    const int                   fSampleCountForNewSurfaces;   // 0 if we don't know
     const SkAlphaType           fAlphaType;
     const SkSurface::Budgeted   fBudgeted;
     mutable SkAtomic<bool>      fAddedRasterVersionToCache;
 
 
     typedef SkImage_Base INHERITED;
 };
 
 #endif