Revert of replace kIgnore_SkAlphaType with kUnknown_SkAlphaType

include/core/SkCanvas.h

 /*
  * Copyright 2006 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkCanvas_DEFINED
 #define SkCanvas_DEFINED
 
@@ skipping 46 matching lines @@
 
     /**
      *  Attempt to allocate raster canvas, matching the ImageInfo, that will draw directly into the
      *  specified pixels. To access the pixels after drawing to them, the caller should call
      *  flush() or call peekPixels(...).
      *
      *  On failure, return NULL. This can fail for several reasons:
      *  1. invalid ImageInfo (e.g. negative dimensions)
      *  2. unsupported ImageInfo for a canvas
      *      - kUnknown_SkColorType, kIndex_8_SkColorType
-     *      - kUnknown_SkAlphaType
+     *      - kIgnore_SkAlphaType
      *      - this list is not complete, so others may also be unsupported
      *
      *  Note: it is valid to request a supported ImageInfo, but with zero
      *  dimensions.
      */
     static SkCanvas* NewRasterDirect(const SkImageInfo&, void*, size_t);
 
     static SkCanvas* NewRasterDirectN32(int width, int height, SkPMColor* pixels, size_t rowBytes) {
         return NewRasterDirect(SkImageInfo::MakeN32Premul(width, height), pixels, rowBytes);
     }
@@ skipping 1413 matching lines @@
 
 class SkCanvasClipVisitor {
 public:
     virtual ~SkCanvasClipVisitor();
     virtual void clipRect(const SkRect&, SkRegion::Op, bool antialias) = 0;
     virtual void clipRRect(const SkRRect&, SkRegion::Op, bool antialias) = 0;
     virtual void clipPath(const SkPath&, SkRegion::Op, bool antialias) = 0;
 };
 
 #endif