Image decoder fixes (mostly) around A8.

src/images/SkScaledBitmapSampler.cpp

Index: src/images/SkScaledBitmapSampler.cpp
diff --git a/src/images/SkScaledBitmapSampler.cpp b/src/images/SkScaledBitmapSampler.cpp
index cad97ead270765a130ef3f70f493f587de04c98d..fb9197ff0300ba2b65590fcec34851687d09e7ef 100644
--- a/src/images/SkScaledBitmapSampler.cpp
+++ b/src/images/SkScaledBitmapSampler.cpp
@@ -549,7 +549,11 @@ static bool Sample_Gray_DA8(void* SK_RESTRICT dstRow,
                             const uint8_t* SK_RESTRICT src,
                             int width, int deltaSrc, int,
                             const SkPMColor[]) {
-    memcpy(dstRow, src, width);
+    // Sampling Gray to A8 uses the same function as Index to Index8,
+    // except we assume that there is alpha for speed, since an A8
+    // bitmap with no alpha is not interesting.
+    (void) Sample_Index_DI(dstRow, src, width, deltaSrc, /* y unused */ 0,
+                           /* ctable unused */ NULL);
     return true;
 }