Speed up toLowerCase, by manually inlining the upper-case part.

runtime/lib/string_patch.dart

Index: runtime/lib/string_patch.dart
diff --git a/runtime/lib/string_patch.dart b/runtime/lib/string_patch.dart
index 717e49db71984f56878bbfcf0cde617c7efb3be5..563dfef978903134bf79622f99f7a1ee62301050 100644
--- a/runtime/lib/string_patch.dart
+++ b/runtime/lib/string_patch.dart
@@ -814,28 +814,20 @@ class _OneByteString extends _StringBase implements String {
     0xf8, 0xf9, 0xfa, 0xfb, 0xfc, 0xfd, 0xfe, 0xff,
   ];
 
-  String _toLowerCaseUpperCaseDetectedAt(int firstUpperCaseIndex) {
-    // String contains upper case characters. Create a new string.
-    final length = this.length;
-    final result = _allocate(length);
-    // First up to firstUpperIndex.
-    int i = 0;
-    for (; i < firstUpperCaseIndex; i++) {
-      result._setAt(i, this.codeUnitAt(i));
-    }
-    for (; i < length; i++) {
-      result._setAt(i, _LC_TABLE[this.codeUnitAt(i)]);
-    }
-    return result;
-  }
-
   String toLowerCase() {
     for (int i = 0; i < this.length; i++) {
       final c = this.codeUnitAt(i);
-      // Ranges: 0x41-0x5a ('A' - 'Z'), 0xc0-0xd6, 0xd8-0xde.
-      if (c != _LC_TABLE[c]) {
-        return _toLowerCaseUpperCaseDetectedAt(i);
+      if (c == _LC_TABLE[c]) continue;
+      // Upper-case character found.
+      final result = _allocate(this.length);
+      for (int j = 0; j < i; j++) {
+        result._setAt(j, this.codeUnitAt(j));
       }
+      for (int j = i; j < this.length; j++) {
+        // Ranges: 0x41-0x5a ('A' - 'Z'), 0xc0-0xd6, 0xd8-0xde.

[Lasse Reichstein Nielsen, 2014/03/26 11:37:51]

Maybe move this comment to the table?
// Upper-case ranges are: ....
// Conversion to lower case performed by adding 0x20.

[Anders Johnsen, 2014/03/26 11:39:12]

Done.

+        result._setAt(j, _LC_TABLE[this.codeUnitAt(j)]);
+      }
+      return result;
     }
     return this;
   }