Add test for new FrontBufferedStream behavior.

src/ports/SkImageDecoder_CG.cpp

 /*
  * Copyright 2008 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkCGUtils.h"
 #include "SkColorPriv.h"
 #include "SkImageDecoder.h"
@@ skipping 22 matching lines @@
     // TODO: use callbacks, so we don't have to load all the data into RAM
     SkAutoMalloc storage;
     const size_t len = SkCopyStreamToStorage(&storage, stream);
     void* data = storage.detach();
 
     return CGDataProviderCreateWithData(data, data, len, malloc_release_proc);
 }
 
 static CGImageSourceRef SkStreamToCGImageSource(SkStream* stream) {
     CGDataProviderRef data = SkStreamToDataProvider(stream);
-    SkASSERT(data);
+    if (!data) {
+        return NULL;
+    }
     CGImageSourceRef imageSrc = CGImageSourceCreateWithDataProvider(data, 0);
     CGDataProviderRelease(data);
     return imageSrc;
 }
 
 class SkImageDecoder_CG : public SkImageDecoder {
 protected:
     virtual Result onDecode(SkStream* stream, SkBitmap* bm, Mode);
 };
 
@@ skipping 292 matching lines @@
 
     SkAutoTCallVProc<const void, CFRelease> arsrc(imageSrc);
     const CFStringRef name = CGImageSourceGetType(imageSrc);
     if (NULL == name) {
         return SkImageDecoder::kUnknown_Format;
     }
     return UTType_to_Format(name);
 }
 
 static SkImageDecoder_FormatReg gFormatReg(get_format_cg);