Make LineSplitter much faster for common case

sdk/lib/convert/line_splitter.dart

Index: sdk/lib/convert/line_splitter.dart
diff --git a/sdk/lib/convert/line_splitter.dart b/sdk/lib/convert/line_splitter.dart
index b5ec32bd6ee94bce6e248a2913cbf5c2e970991a..eddb800691e1333317a835bbc51a58fd0b6d3b3a 100644
--- a/sdk/lib/convert/line_splitter.dart
+++ b/sdk/lib/convert/line_splitter.dart
@@ -49,7 +49,29 @@ class LineSplitter extends Converter<String, List<String>> {
     }
   }
 
-  List<String> convert(String data) => split(data).toList();
+  List<String> convert(String data) {
+    List lines = new List();

[Lasse Reichstein Nielsen, 2016/03/08 10:48:16]

List<String> lines = <String>[];

[hausner, 2016/03/08 18:35:08]

Done.

+    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));

[Lasse Reichstein Nielsen, 2016/03/08 10:48:16]

remove "end", just:
  lines.add(data.substring(sliceStart));

[hausner, 2016/03/08 18:35:08]

I like explicit parameters. Makes it clear(er) at the call site what's
happening.

+    }
+    return lines;
+  }
 
   StringConversionSink startChunkedConversion(Sink<String> sink) {
     if (sink is! StringConversionSink) {