Add Alpha8 support to SkPNGImageEncoder

src/codec/SkAndroidCodec.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 "SkAndroidCodec.h"
 #include "SkCodec.h"
 #include "SkCodecPriv.h"
@@ skipping 68 matching lines @@
         case kIndex_8_SkColorType:
             if (kIndex_8_SkColorType == suggestedColorType) {
                 return kIndex_8_SkColorType;
             }
             break;
         case kAlpha_8_SkColorType:
             // Fall through to kGray_8.  Before kGray_8_SkColorType existed,
             // we allowed clients to request kAlpha_8 when they wanted a
             // grayscale decode.
         case kGray_8_SkColorType:
-            if (kGray_8_SkColorType == suggestedColorType) {
+            if (kGray_8_SkColorType == suggestedColorType ||
+                kAlpha_8_SkColorType == suggestedColorType)
+            {
                 return kGray_8_SkColorType;
             }
             break;
         case kRGB_565_SkColorType:
             if (kOpaque_SkAlphaType == this->getInfo().alphaType()) {
                 return kRGB_565_SkColorType;
             }
             break;
         default:
             break;
     }
 
-    // Android has limited support for kGray_8 (using kAlpha_8).  We will not
-    // use kGray_8 for Android unless they specifically ask for it.
-    if (kGray_8_SkColorType == suggestedColorType) {
+    // Android has limited support for kGray_8 and kAlpha_8.  We will not use these types for
+    // Android unless they specifically ask for it.
+    if (kGray_8_SkColorType == suggestedColorType || kAlpha_8_SkColorType == suggestedColorType) {
         return kN32_SkColorType;
     }
 
     // This may be kN32_SkColorType or kIndex_8_SkColorType.
     return suggestedColorType;
 }
 
 SkAlphaType SkAndroidCodec::computeOutputAlphaType(bool requestedUnpremul) {
     if (kOpaque_SkAlphaType == this->getInfo().alphaType()) {
         return kOpaque_SkAlphaType;
@@ skipping 73 matching lines @@
         }
     }
 
     return this->onGetAndroidPixels(info, pixels, rowBytes, *options);
 }
 
 SkCodec::Result SkAndroidCodec::getAndroidPixels(const SkImageInfo& info, void* pixels,
         size_t rowBytes) {
     return this->getAndroidPixels(info, pixels, rowBytes, nullptr);
 }