Fix bug in SkGifCodec / Switch SkImageDec tests to use Codec

tests/CodecPriv.h

+/*
+ * Copyright 2016 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "SkBitmap.h"
+#include "SkCodec.h"
+#include "SkData.h"
+
+inline bool decode_memory(const void* mem, size_t size, SkBitmap* bm) {
+    SkAutoTUnref<SkData> data(SkData::NewWithoutCopy(mem, size));
+
+    SkAutoTDelete<SkCodec> codec(SkCodec::NewFromData(data.get()));
+    if (!codec) {
+        return false;
+    }
+
+    // Construct a color table for the decode if necessary
+    SkAutoTUnref<SkColorTable> colorTable(nullptr);
+    SkPMColor* colorPtr = nullptr;
+    int* colorCountPtr = nullptr;
+    int maxColors = 256;
+    if (kIndex_8_SkColorType == codec->getInfo().colorType()) {
+        SkPMColor colors[256];
+        colorTable.reset(new SkColorTable(colors, maxColors));
+        colorPtr = const_cast<SkPMColor*>(colorTable->readColors());
+        colorCountPtr = &maxColors;
+    }
+
+    bm->allocPixels(codec->getInfo(), nullptr, colorTable.get());
+    const SkCodec::Result result = codec->getPixels(codec->getInfo(), bm->getPixels(),
+            bm->rowBytes(), nullptr, colorPtr, colorCountPtr);
+    return result == SkCodec::kSuccess || result == SkCodec::kIncompleteInput;
+}