Add support for multiple frames in SkCodec

src/codec/SkStreamBuffer.cpp

+/*
+ * 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 "SkStreamBuffer.h"
+
+SkStreamBuffer::SkStreamBuffer(SkStream* stream)
+    : fStream(stream)
+    , fBytesBuffered(0)
+{}
+
+size_t SkStreamBuffer::buffer(size_t bytesToBuffer) {
+    // FIXME (scroggo): What should we do if the client tries to read too much?
+    // Should not be a problem in GIF.
+    SkASSERT(fBytesBuffered + bytesToBuffer <= kMaxSize);
+
+    const size_t bytesBuffered = fStream->read(fBuffer + fBytesBuffered, bytesToBuffer);
+    fBytesBuffered += bytesBuffered;
+    return bytesBuffered;
+}