Update CodexTest to test valid_alpha.

src/codec/SkCodec_wbmp.cpp

Index: src/codec/SkCodec_wbmp.cpp
diff --git a/src/codec/SkCodec_wbmp.cpp b/src/codec/SkCodec_wbmp.cpp
index 86dce5cc89e95590f8d0d138df9bda352994f95d..69ef7d4091d0aa3f6f3c514185c0cc2ca70277e8 100644
--- a/src/codec/SkCodec_wbmp.cpp
+++ b/src/codec/SkCodec_wbmp.cpp
@@ -128,6 +128,10 @@ SkCodec::Result SkWbmpCodec::onGetPixels(const SkImageInfo& info,
         return kInvalidScale;
     }
 
+    if (!valid_alpha(info.alphaType(), this->getInfo().alphaType())) {
+        return SkCodec::kInvalidConversion;
+    }
+
     // Prepare a color table if necessary
     setup_color_table(info.colorType(), ctable, ctableCount);
 
@@ -208,6 +212,10 @@ public:
             return SkCodec::kInvalidScale;
         }
 
+        if (!valid_alpha(dstInfo.alphaType(), this->getInfo().alphaType())) {
+            return SkCodec::kInvalidConversion;
+        }
+
         // Fill in the color table
         setup_color_table(dstInfo.colorType(), inputColorTable, inputColorCount);