Add LibraryIndex class for finding classes and members by name.

pkg/kernel/lib/transformations/mixin_full_resolution.dart

Index: pkg/kernel/lib/transformations/mixin_full_resolution.dart
diff --git a/pkg/kernel/lib/transformations/mixin_full_resolution.dart b/pkg/kernel/lib/transformations/mixin_full_resolution.dart
index 7f200102ee61bad7ff5b1f5c87e14fb76f295ee1..7f92ce9cf296fada7085e3013f95df9ab1ba3ec0 100644
--- a/pkg/kernel/lib/transformations/mixin_full_resolution.dart
+++ b/pkg/kernel/lib/transformations/mixin_full_resolution.dart
@@ -271,7 +271,7 @@ class SuperCallResolutionTransformer extends Transformer {
   ConstructorInvocation _createInvocation(String methodName,
       Arguments callArguments, bool isSuperInvocation, Expression receiver) {
     if (_invocationMirrorConstructor == null) {
-      Class clazz = coreTypes.getCoreClass('dart:core', '_InvocationMirror');
+      Class clazz = coreTypes.getClass('dart:core', '_InvocationMirror');
       _invocationMirrorConstructor = clazz.constructors[0];
     }
 
@@ -315,10 +315,7 @@ class SuperCallResolutionTransformer extends Transformer {
 
   /// Create a fixed length list containing given expressions.
   Expression _fixedLengthList(List<Expression> list) {
-    if (_listFrom == null) {
-      Class clazz = coreTypes.getCoreClass('dart:core', 'List');
-      _listFrom = clazz.procedures.firstWhere((c) => c.name.name == "from");
-    }
+    _listFrom ??= coreTypes.getMember('dart:core', 'List', 'from');
     return new StaticInvocation(
         _listFrom,
         new Arguments([new ListLiteral(list)],