add ImageShader, sharing code with its Bitmap cousin

src/image/SkImage_Gpu.cpp

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkBitmapCache.h"
 #include "SkImage_Gpu.h"
 #include "GrContext.h"
@@ skipping 31 matching lines @@
     const SkSurface::Budgeted budgeted = SkSurface::kNo_Budgeted;
     return SkSurface::NewRenderTarget(ctx, budgeted, info, fSampleCountForNewSurfaces, &props);
 }
 
 extern void SkTextureImageApplyBudgetedDecision(SkImage* image) {
     if (as_IB(image)->getTexture()) {
         ((SkImage_Gpu*)image)->applyBudgetDecision();
     }
 }
 
-SkShader* SkImage_Gpu::onNewShader(SkShader::TileMode tileX, SkShader::TileMode tileY,
-                                   const SkMatrix* localMatrix) const {
-    SkBitmap bm;
-    GrWrapTextureInBitmap(fTexture, this->width(), this->height(), this->isOpaque(), &bm);
-    return SkShader::CreateBitmapShader(bm, tileX, tileY, localMatrix);
-}
-
 bool SkImage_Gpu::getROPixels(SkBitmap* dst) const {
     if (SkBitmapCache::Find(this->uniqueID(), dst)) {
         SkASSERT(dst->getGenerationID() == this->uniqueID());
         SkASSERT(dst->isImmutable());
         SkASSERT(dst->getPixels());
         return true;
     }
 
     SkAlphaType at = this->isOpaque() ? kOpaque_SkAlphaType : kPremul_SkAlphaType;
     if (!dst->tryAllocPixels(SkImageInfo::MakeN32(this->width(), this->height(), at))) {
@@ skipping 211 matching lines @@
     if (!dst) {
         return nullptr;
     }
     
     const SkIRect srcR = SkIRect::MakeWH(desc.fWidth, desc.fHeight);
     const SkIPoint dstP = SkIPoint::Make(0, 0);
     ctx->copySurface(dst, src, srcR, dstP, GrContext::kFlushWrites_PixelOp);
     return dst;
 }