Add a buffered SkStream class.

include/utils/SkBufferedStream.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.
+ */
+
+#include "SkStream.h"
+#include "SkTypes.h"
+
+class SkBufferedStream : public SkStreamRewindable {

[reed1, 2013/09/17 20:23:02]

We might consider just adding the static Create to SkStream itself, and hiding
*all* of this detail inside the imp.

e.g.

class SkStream ... {
...
    static SkStream* CreateBufferedStream(SkStream* other, size_t ...);
...
};

[scroggo, 2013/09/17 20:41:19]

I was leaving it in utils since I think only Android needs it, but if we want it
in core that is fine with me too.

+public:
+    /**
+     *  Creates a new stream that wraps and buffers SkStream.
+     *  @param stream SkStream to buffer. If NULL, NULL is returned. After
+     *      this call, unref stream and do not refer to it.
+     *      SkBufferedStream is expected to be its only owner.
+     *  @param bufferSize Exact size of the buffer to be used.
+     *  @return An SkStream that can buffer up to bufferSize.
+     */
+    static SkBufferedStream* Create(SkStream* stream, size_t bufferSize);
+
+    virtual size_t read(void* buffer, size_t size) SK_OVERRIDE;
+
+    virtual bool isAtEnd() const SK_OVERRIDE;
+
+    virtual bool rewind() SK_OVERRIDE;
+
+    virtual bool hasPosition() const SK_OVERRIDE { return true; }
+
+    virtual size_t getPosition() const SK_OVERRIDE { return fOffset; }
+
+    virtual bool hasLength() const SK_OVERRIDE;
+
+    virtual size_t getLength() const SK_OVERRIDE;
+
+    virtual SkStreamRewindable* duplicate() const SK_OVERRIDE { return NULL; }
+
+private:
+    SkAutoTUnref<SkStream>  fStream;
+    size_t                  fOffset;
+    size_t                  fBufferedSoFar;
+    const size_t            fBufferSize;
+    SkAutoTMalloc<char>     fBuffer;
+
+    // Unimplemented.
+    SkBufferedStream();
+
+    // Private. Use Create.
+    SkBufferedStream(SkStream*, size_t bufferSize);
+
+    char* getBufferAtOffset() {
+        return fBuffer.get() + fOffset;
+    }
+
+    typedef SkStream INHERITED;
+};