Document SkSurface::MakeRaster's memory initialization

tests/SurfaceTest.cpp

 /*
  * Copyright 2013 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 "SkCanvas.h"
 #include "SkData.h"
@@ skipping 733 matching lines @@
     auto surf1(SkSurface::MakeRaster(info, 500, nullptr));
     check_rowbytes_remain_consistent(surf1.get(), reporter);
 
     // Try some illegal rowByte values
     auto s = SkSurface::MakeRaster(info, 396, nullptr);    // needs to be at least 400
     REPORTER_ASSERT(reporter, nullptr == s);
     s = SkSurface::MakeRaster(info, 1 << 30, nullptr); // allocation to large
     REPORTER_ASSERT(reporter, nullptr == s);
 }
 
+DEF_TEST(surface_raster_zeroinitialized, reporter) {
+    sk_sp<SkSurface> s(SkSurface::MakeRasterN32Premul(100, 100));
+    SkPixmap pixmap;
+    REPORTER_ASSERT(reporter, s->peekPixels(&pixmap));
+
+    for (int i = 0; i < pixmap.info().width(); ++i) {
+        for (int j = 0; j < pixmap.info().height(); ++j) {
+            REPORTER_ASSERT(reporter, *pixmap.addr32(i, j) == 0);
+        }
+    }
+}
+
 #if SK_SUPPORT_GPU
 static sk_sp<SkSurface> create_gpu_surface_backend_texture(
     GrContext* context, int sampleCnt, uint32_t color, GrBackendObject* outTexture) {
     const int kWidth = 10;
     const int kHeight = 10;
     SkAutoTDeleteArray<uint32_t> pixels(new uint32_t[kWidth * kHeight]);
     sk_memset32(pixels.get(), color, kWidth * kHeight);
     GrBackendTextureDesc desc;
     desc.fConfig = kRGBA_8888_GrPixelConfig;
     desc.fWidth = kWidth;
@@ skipping 194 matching lines @@
             // our surface functions.
             GrRenderTarget* rt = surface->getCanvas()->internal_private_accessTopLayerDrawContext()
                 ->accessRenderTarget();
             REPORTER_ASSERT(reporter,
                             ctxInfo.grContext()->resourceProvider()->attachStencilAttachment(rt));
             gpu->deleteTestingOnlyBackendTexture(textureObject);
         }
     }
 }
 #endif