Merge the dart:uri library into dart:core and update the Uri class

sdk/lib/core/core.dart

Index: sdk/lib/core/core.dart
diff --git a/sdk/lib/core/core.dart b/sdk/lib/core/core.dart
index 391000c8a0533fd30fdec5be3c2142de5a62a3c5..de7fc4aa2e05288df5be832af252619f515a59ee 100644
--- a/sdk/lib/core/core.dart
+++ b/sdk/lib/core/core.dart
@@ -7,6 +7,7 @@ library dart.core;
 import "dart:collection";
 import "dart:_collection-dev" hide Symbol;
 import "dart:_collection-dev" as _collection_dev;
+import "dart:utf" show codepointsToUtf8, decodeUtf8;
 
 part "bool.dart";
 part "comparable.dart";
@@ -37,3 +38,4 @@ part "string_buffer.dart";
 part "string_sink.dart";
 part "symbol.dart";
 part "type.dart";
+part "uri.dart";