Update CodexTest to test valid_alpha.

Add a static function to CodexTest, which consolidates decoding,
comparing to an expected SkCodec::Result, and optionally comparing to a
digest.

Test decoding non-opaque to opaque (fails) and premul to unpremul/vice
versa (succeeds).

BUG=skia:3475

Review URL: https://codereview.chromium.org/1277253003

1 files changed, 8 insertions, 0 deletions

diff --git a/src/codec/SkCodec_wbmp.cpp b/src/codec/SkCodec_wbmp.cpp
index 52535e1f02..6f98294fc6 100644
--- a/src/codec/SkCodec_wbmp.cpp
+++ b/src/codec/SkCodec_wbmp.cpp
@@ -120,6 +120,10 @@ 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);
 
@@ -200,6 +204,10 @@ 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);