Add a test for decoding a gif with sampleSize 4.

tests/GifTest.cpp

Index: tests/GifTest.cpp
diff --git a/tests/GifTest.cpp b/tests/GifTest.cpp
index e2e03845cad5f2c9a18f9b9f64c4b0e149b7120d..978e3745394dffe291ee662770e5fa903a531eee 100644
--- a/tests/GifTest.cpp
+++ b/tests/GifTest.cpp
@@ -5,12 +5,15 @@
  * found in the LICENSE file.
  */
 
+#include "SkTypes.h"
+
 // This tests out GIF decoder (SkImageDecoder_libgif.cpp)
 // It is not used on these platforms:
 #if (!defined(SK_BUILD_FOR_WIN32)) &&           \
     (!defined(SK_BUILD_FOR_IOS)) &&             \
     (!defined(SK_BUILD_FOR_MAC))
 
+#include "Resources.h"
 #include "SkBitmap.h"
 #include "SkData.h"
 #include "SkForceLinking.h"
@@ -197,4 +200,25 @@ DEF_TEST(Gif, reporter) {
     // "libgif warning [interlace DGifGetLine]"
 }
 
+// Regression test for decoding a gif image with sampleSize of 4, which was
+// previously crashing.
+DEF_TEST(Gif_Sampled, r) {
+    SkFILEStream fileStream(GetResourcePath("test640x479.gif").c_str());
+    REPORTER_ASSERT(r, fileStream.isValid());
+    if (!fileStream.isValid()) {
+        return;
+    }
+
+    SkAutoTDelete<SkImageDecoder> decoder(SkImageDecoder::Factory(&fileStream));
+    REPORTER_ASSERT(r, decoder);
+    if (!decoder) {
+        return;
+    }
+    decoder->setSampleSize(4);
+    SkBitmap bm;
+    const SkImageDecoder::Result result = decoder->decode(&fileStream, &bm,
+            SkImageDecoder::kDecodePixels_Mode);
+    REPORTER_ASSERT(r, result == SkImageDecoder::kSuccess);
+}
+
 #endif  // !(SK_BUILD_FOR_WIN32||SK_BUILD_FOR_IOS||SK_BUILD_FOR_MAC)