Add chunked conversion to converters.

sdk/lib/convert/converter.dart

Index: sdk/lib/convert/converter.dart
diff --git a/sdk/lib/convert/converter.dart b/sdk/lib/convert/converter.dart
index 8e7a6f164f9a5b8aae3319d3b58ca15456a53f8d..faa509b944c3ec22e5e702c2b4e35d3eb9485f8e 100644
--- a/sdk/lib/convert/converter.dart
+++ b/sdk/lib/convert/converter.dart
@@ -25,6 +25,39 @@ abstract class Converter<S, T> {
   Converter<S, dynamic> fuse(Converter<T, dynamic> other) {
     return new _FusedConverter<S, T, dynamic>(this, other);
   }
+
+  /**
+   * Starts a chunked conversion.
+   *
+   * The returned [ChunkedConversionSink] supports the interface described by
+   * [inputInterface].
+   *
+   * If the given [sink] supports the methods described by
+   * [outputInterface] then the chunked conversion can take advantage of
+   * the additional methods and provide a more efficient conversion.
+   *
+   * If [sink] does not support the [outputInterface] it is adapted. If
+   * necessary, the adapter buffers all chunks and invokes
+   * `addNonChunked` on [sink].
+   */
+  ChunkedConversionSink startChunkedConversion(ChunkedConversionSink sink) {
+    throw new UnsupportedError(
+        "This converter does not support chunked conversions: $this");
+  }
+
+  /**
+   * Defines the accepted input interface for chunked conversions.
+   *
+   * Is `null` if `this` does not support chunked conversions.
+   */
+  ChunkedConversionInterface get inputInterface => null;
+
+  /**
+   * Defines the accepted output interface for chunked conversions.
+   *
+   * Is `null` if `this` does not support chunked conversions.
+   */
+  ChunkedConversionInterface get outputInterface => null;
 }
 
 /**
@@ -39,4 +72,19 @@ class _FusedConverter<S, M, T> extends Converter<S, T> {
   _FusedConverter(this._first, this._second);
 
   T convert(S input) => _second.convert(_first.convert(input));
+
+  ChunkedConversionSink startChunkedConversion(ChunkedConversionSink sink) {
+    return _first.startChunkedConversion(_second.startChunkedConversion(sink));
+  }
+
+  ChunkedConversionInterface get inputInterface {
+    // Don't advertise a chunked conversion if the _second converter doesn't
+    // support it.
+    if (_second.inputInterface != null) return _first.inputInterface;
+  }
+  ChunkedConversionInterface get outputInterface {
+    // Don't advertise a chunked conversion if the _first converter doesn't
+    // support it.
+    if (_first.outputInterface != null) return _second.outputInterface;
+  }
 }