Don't copy image buffer when calculating size.

tests/ImageTest.cpp

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include <functional>
 #include <initializer_list>
 #include <vector>
@@ skipping 902 matching lines @@
         { [context] { return create_gpu_image(context); },
           {{SkMatrix::I(), kNone_SkFilterQuality, 0}},
           kNone_SkFilterQuality, 1, false },
         // Create a texture image in a another GrContext.
         { [testContext, otherContextInfo] {
             otherContextInfo.testContext()->makeCurrent();
             sk_sp<SkImage> otherContextImage = create_gpu_image(otherContextInfo.grContext());
             testContext->makeCurrent();
             return otherContextImage;
           }, {{SkMatrix::I(), kNone_SkFilterQuality, 0}},
-        kNone_SkFilterQuality, 1, false },
+        kNone_SkFilterQuality, 1, true },
         // Create an image that is too large to upload.
         { create_image_large,    {{SkMatrix::I(), kNone_SkFilterQuality, 0}},
           kNone_SkFilterQuality, 1, false },
         // Create an image that is too large, but is scaled to an acceptable size.
         { create_image_large, {{SkMatrix::I(), kMedium_SkFilterQuality, 4}},
           kMedium_SkFilterQuality, 16, true},
         // Create an image with multiple low filter qualities, make sure we round up.
         { create_image_large, {{SkMatrix::I(), kNone_SkFilterQuality, 4},
                                {SkMatrix::I(), kMedium_SkFilterQuality, 4}},
           kMedium_SkFilterQuality, 16, true},
@@ skipping 108 matching lines @@
     SkBitmap bm1;
     bm1.allocPixels(SkImageInfo::MakeN32(256, 256, kUnpremul_SkAlphaType));
     bm0.readPixels(bm1.info(), bm1.getPixels(), bm1.rowBytes(), 0, 0);
 
     SkBitmap bm2;
     bm2.allocPixels(SkImageInfo::MakeN32(256, 256, kPremul_SkAlphaType));
     bm1.readPixels(bm2.info(), bm2.getPixels(), bm2.rowBytes(), 0, 0);
 
     REPORTER_ASSERT(reporter, equal(bm0, bm2));
 }