Avoid getLength in ico decoder.

src/images/SkStreamHelpers.h

+/*
+ * Copyright 2013 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef SkStreamHelpers_DEFINED
+#define SkStreamHelpers_DEFINED
+
+class SkAutoMalloc;
+class SkStream;
+
+/**
+ *  Copy the provided stream to memory allocated by storage.
+ *  Used by SkImageDecoder_libbmp and SkImageDecoder_libico.
+ *  @param storage Allocator to hold the memory. Will be reset to be large
+ *      enough to hold the entire stream. Upon successful return,
+ *      storage->get() will point to data holding the SkStream's entire
+ *      contents.
+ *  @param stream SkStream to be copied into storage.
+ *  @return size_t Total number of bytes in the SkStream, which is also the
+ *      number of bytes pointed to by storage->get(). Returns 0 on failure.
+ */
+size_t CopyStreamToStorage(SkAutoMalloc* storage, SkStream* stream);
+
+#endif // SkStreamHelpers_DEFINED