Updates to skimage tool to use it for testing.

src/images/SkImageDecoder_libwebp.cpp

Index: src/images/SkImageDecoder_libwebp.cpp
diff --git a/src/images/SkImageDecoder_libwebp.cpp b/src/images/SkImageDecoder_libwebp.cpp
index d9434c281396c1cfe03ba9d05cdc71d0993e98d2..1618eb1e5fe54a80abc9ab8ea5708bb2da8aee14 100644
--- a/src/images/SkImageDecoder_libwebp.cpp
+++ b/src/images/SkImageDecoder_libwebp.cpp
@@ -113,6 +113,7 @@ protected:
     virtual bool onBuildTileIndex(SkStream *stream, int *width, int *height) SK_OVERRIDE;
     virtual bool onDecodeRegion(SkBitmap* bitmap, const SkIRect& rect) SK_OVERRIDE;
     virtual bool onDecode(SkStream* stream, SkBitmap* bm, Mode) SK_OVERRIDE;
+    virtual Format onGetFormat(SkStream*) const SK_OVERRIDE;
 
 private:
     bool setDecodeConfig(SkBitmap* decodedBitmap, int width, int height);
@@ -124,6 +125,14 @@ private:
     typedef SkImageDecoder INHERITED;
 };
 
+SkImageDecoder::Format SkWEBPImageDecoder::onGetFormat(SkStream* stream) const {
+    int width, height, hasAlpha;
+    if (webp_parse_header(stream, &width, &height, &hasAlpha)) {
+        return kWEBP_Format;
+    }
+    return kUnknown_Format;
+}
+
 //////////////////////////////////////////////////////////////////////////
 
 #ifdef TIME_DECODE