leave pixel memory uninitialized for opaque alpha type in SkSurface::MakeRaster

src/image/SkSurface_Raster.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 "SkSurface_Base.h"
 #include "SkImagePriv.h"
 #include "SkCanvas.h"
@@ skipping 190 matching lines @@
                                              const SkSurfaceProps* props) {
     return MakeRasterDirectReleaseProc(info, pixels, rowBytes, nullptr, nullptr, props);
 }
 
 sk_sp<SkSurface> SkSurface::MakeRaster(const SkImageInfo& info, size_t rowBytes,
                                        const SkSurfaceProps* props) {
     if (!SkSurface_Raster::Valid(info)) {
         return nullptr;
     }
 
-    SkAutoTUnref<SkPixelRef> pr(SkMallocPixelRef::NewZeroed(info, rowBytes, nullptr));
+    // If the requested alpha type is opaque, then leave the pixels uninitialized.
+    // Alpha formats can be safely initialiezd to zero.
+    SkAutoTUnref<SkPixelRef> pr(info.isOpaque()
+                                ? SkMallocPixelRef::NewAllocate(info, rowBytes, nullptr)
+                                : SkMallocPixelRef::NewZeroed(info, rowBytes, nullptr));
     if (nullptr == pr.get()) {
         return nullptr;
     }
     if (rowBytes) {
         SkASSERT(pr->rowBytes() == rowBytes);
     }
     return sk_make_sp<SkSurface_Raster>(pr, props);
 }