Updates to skimage tool to use it for testing.

src/images/SkImageDecoder_libgif.cpp

Index: src/images/SkImageDecoder_libgif.cpp
diff --git a/src/images/SkImageDecoder_libgif.cpp b/src/images/SkImageDecoder_libgif.cpp
index 3e4cda8a0bac26611ca1760c3da18aeaaf0f973c..1553af27c1d95bf7f5de7378c537d3671756d32d 100644
--- a/src/images/SkImageDecoder_libgif.cpp
+++ b/src/images/SkImageDecoder_libgif.cpp
@@ -22,6 +22,8 @@ public:
         return kGIF_Format;
     }
 
+    virtual Format onGetFormat(SkStream*) const SK_OVERRIDE;
+
 protected:
     virtual bool onDecode(SkStream* stream, SkBitmap* bm, Mode mode) SK_OVERRIDE;
 
@@ -91,9 +93,6 @@ private:
 
 ///////////////////////////////////////////////////////////////////////////////
 
-//#define GIF_STAMP       "GIF"    /* First chars in file - GIF stamp. */
-//#define GIF_STAMP_LEN   (sizeof(GIF_STAMP) - 1)
-
 static int DecodeCallBackProc(GifFileType* fileType, GifByteType* out,
                               int size) {
     SkStream* stream = (SkStream*) fileType->UserData;
@@ -361,6 +360,25 @@ DONE:
     return true;
 }
 
+static bool is_gif(SkStream* stream) {
+    char buf[GIF_STAMP_LEN];
+    if (stream->read(buf, GIF_STAMP_LEN) == GIF_STAMP_LEN) {
+        if (memcmp(GIF_STAMP,   buf, GIF_STAMP_LEN) == 0 ||
+                memcmp(GIF87_STAMP, buf, GIF_STAMP_LEN) == 0 ||
+                memcmp(GIF89_STAMP, buf, GIF_STAMP_LEN) == 0) {
+            return true;
+        }
+    }
+    return false;
+}
+
+SkImageDecoder::Format SkGIFImageDecoder::onGetFormat(SkStream* stream) const {
+    if (is_gif(stream)) {
+        return kGIF_Format;
+    }
+    return kUnknown_Format;
+}
+
 ///////////////////////////////////////////////////////////////////////////////
 DEFINE_DECODER_CREATOR(GIFImageDecoder);
 ///////////////////////////////////////////////////////////////////////////////
@@ -368,13 +386,8 @@ DEFINE_DECODER_CREATOR(GIFImageDecoder);
 #include "SkTRegistry.h"
 
 static SkImageDecoder* sk_libgif_dfactory(SkStream* stream) {
-    char buf[GIF_STAMP_LEN];
-    if (stream->read(buf, GIF_STAMP_LEN) == GIF_STAMP_LEN) {
-        if (memcmp(GIF_STAMP,   buf, GIF_STAMP_LEN) == 0 ||
-                memcmp(GIF87_STAMP, buf, GIF_STAMP_LEN) == 0 ||
-                memcmp(GIF89_STAMP, buf, GIF_STAMP_LEN) == 0) {
-            return SkNEW(SkGIFImageDecoder);
-        }
+    if (is_gif(stream)) {
+        return SkNEW(SkGIFImageDecoder);
     }
     return NULL;
 }