Make LineSplitter much faster for common case

sdk/lib/convert/line_splitter.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of dart.convert;
 
 // Character constants.
 const int _LF = 10;
 const int _CR = 13;
 
@@ skipping 31 matching lines @@
         }
       }
       yield lines.substring(sliceStart, i);
       sliceStart = i + 1;
     }
     if (sliceStart < end) {
       yield lines.substring(sliceStart, end);
     }
   }
 
-  List<String> convert(String data) => split(data).toList();
+  List<String> convert(String data) {
+    List<String> lines = <String>[];
+    int end = data.length;
+    int sliceStart = 0;
+    int char = 0;
+    for (int i = 0; i < end; i++) {
+      int previousChar = char;
+      char = data.codeUnitAt(i);
+      if (char != _CR) {
+        if (char != _LF) continue;
+        if (previousChar == _CR) {
+          sliceStart = i + 1;
+          continue;
+        }
+      }
+      lines.add(data.substring(sliceStart, i));
+      sliceStart = i + 1;
+    }
+    if (sliceStart < end) {
+      lines.add(data.substring(sliceStart, end));
+    }
+    return lines;
+  }
 
   StringConversionSink startChunkedConversion(Sink<String> sink) {
     if (sink is! StringConversionSink) {
       sink = new StringConversionSink.from(sink);
     }
     return new _LineSplitterSink(sink);
   }
 
   // Override the base-class' bind, to provide a better type.
   Stream<String> bind(Stream<String> stream) => super.bind(stream);
@@ skipping 67 matching lines @@
       _sink.add(lines.substring(sliceStart, i));
       sliceStart = i + 1;
     }
     if (sliceStart < end) {
       _carry = lines.substring(sliceStart, end);
     } else {
       _skipLeadingLF = (char == _CR);
     }
   }
 }