extract some common code from PictureRenderer

src/utils/SkDataUtils.h

+/*
+ * Copyright 2014 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef SkDataUtils_DEFINED
+#define SkDataUtils_DEFINED
+
+#include "SkData.h"
+#include "SkStream.h"
+
+/**
+ * Static class that performs various operations on SkData objects.
+ *
+ * EPOGER: Before committing, add unittests for these methods.
+ *
+ * TODO(epoger): Move these methods into SkStream.[cpp|h], as attempted in
+ * https://codereview.appspot.com/7300071 ?
+ */
+class SkDataUtils {
+public:
+    /**
+     * Read as many bytes as possible (up to maxBytes) from the stream into
+     * an SkData object.
+     *
+     * If the returned SkData contains fewer than maxBytes, then EOF has been
+     * reached and no more data would be available from subsequent calls.
+     * (If EOF has already been reached, then this call will return an empty
+     * SkData object immediately.)
+     *
+     * If there are fewer than maxBytes bytes available to read from the
+     * stream, but the stream has not been closed yet, this call will block
+     * until there are enough bytes to read or the stream has been closed.
+     *
+     * It is up to the caller to call unref() on the returned SkData object
+     * once the data is no longer needed, so that the underlying buffer will
+     * be freed.  For example:
+     *
+     * {
+     *   size_t maxBytes = 256;
+     *   SkAutoDataUnref dataRef(readIntoSkData(stream, maxBytes));
+     *   if (NULL != dataRef.get()) {
+     *     size_t bytesActuallyRead = dataRef.get()->size();
+     *     // use the data...
+     *   }
+     * }
+     * // underlying buffer has been freed, thanks to auto unref
+     */
+    static SkData* ReadIntoSkData(SkStream &stream, size_t maxBytes);
+
+    /**
+     * Wrapper around ReadIntoSkData for files: reads the entire file into
+     * an SkData object.
+     */
+    static SkData* ReadFileIntoSkData(SkFILEStream &stream) {
+        return ReadIntoSkData(stream, stream.getLength());
+    }
+
+};
+
+#endif