Add Alpha8 support to SkPNGImageEncoder

src/codec/SkAndroidCodec.cpp

Index: src/codec/SkAndroidCodec.cpp
diff --git a/src/codec/SkAndroidCodec.cpp b/src/codec/SkAndroidCodec.cpp
index db365642327cc1041f1dbda911ed2d87c9c57da1..fe96c5a65ff90a8aa8273001f17558a19038de42 100644
--- a/src/codec/SkAndroidCodec.cpp
+++ b/src/codec/SkAndroidCodec.cpp
@@ -86,7 +86,9 @@ SkColorType SkAndroidCodec::computeOutputColorType(SkColorType requestedColorTyp
             // 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;
@@ -99,9 +101,9 @@ SkColorType SkAndroidCodec::computeOutputColorType(SkColorType requestedColorTyp
             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;
     }