Update CodexTest to test valid_alpha.

src/codec/SkCodec_wbmp.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 "SkCodec.h"
 #include "SkCodecPriv.h"
 #include "SkColorPriv.h"
@@ skipping 110 matching lines @@
         return kCouldNotRewind;
     }
     if (options.fSubset) {
         // Subsets are not supported.
         return kUnimplemented;
     }
     if (info.dimensions() != this->getInfo().dimensions()) {
         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);
 
 
     // Initialize the swizzler
     SkAutoTDelete<SkSwizzler> swizzler(this->initializeSwizzler(info, ctable, options));
     if (NULL == swizzler.get()) {
         return kInvalidConversion;
     }
 
@@ skipping 60 matching lines @@
             return SkCodec::kCouldNotRewind;
         }
         if (options.fSubset) {
             // Subsets are not supported.
             return SkCodec::kUnimplemented;
         }
         if (dstInfo.dimensions() != this->getInfo().dimensions()) {
             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);
 
         // Copy the color table to a pointer that can be owned by the scanline decoder
         if (kIndex_8_SkColorType == dstInfo.colorType()) {
             fColorTable.reset(SkNEW_ARGS(SkColorTable, (inputColorTable, 2)));
         }
 
         // Initialize the swizzler
         fSwizzler.reset(fCodec->initializeSwizzler(dstInfo,
@@ skipping 17 matching lines @@
 SkScanlineDecoder* SkWbmpCodec::NewSDFromStream(SkStream* stream) {
     SkAutoTDelete<SkWbmpCodec> codec(static_cast<SkWbmpCodec*>(
             SkWbmpCodec::NewFromStream(stream)));
     if (!codec) {
         return NULL;
     }
 
     // Return the new scanline decoder
     return SkNEW_ARGS(SkWbmpScanlineDecoder, (codec.detach()));
 }