Introduce ClassLike, MemberLike, FieldLike and FunctionLike

pkg/compiler/lib/src/ssa/kernel_ast_adapter.dart

Index: pkg/compiler/lib/src/ssa/kernel_ast_adapter.dart
diff --git a/pkg/compiler/lib/src/ssa/kernel_ast_adapter.dart b/pkg/compiler/lib/src/ssa/kernel_ast_adapter.dart
index 71f6b549506b5da5d671887ea0bcbc6e9d3603f1..be4a558e28399c9f6fec6d62f62fa0c5dfdb156a 100644
--- a/pkg/compiler/lib/src/ssa/kernel_ast_adapter.dart
+++ b/pkg/compiler/lib/src/ssa/kernel_ast_adapter.dart
@@ -76,6 +76,7 @@ class KernelAstAdapter {
     return constantValue;
   }
 
+  // TODO(johnniwinther): Use the more precise functions below.
   Element getElement(ir.Node node) {
     Element result = _nodeToElement[node];
     assert(invariant(CURRENT_ELEMENT_SPANNABLE, result != null,
@@ -83,6 +84,12 @@ class KernelAstAdapter {
     return result;
   }
 
+  MemberElement getMember(ir.Node node) => getElement(node).declaration;
+
+  MethodElement getMethod(ir.Node node) => getElement(node).declaration;
+
+  ClassElement getClass(ir.Node node) => getElement(node).declaration;
+
   ast.Node getNode(ir.Node node) {
     ast.Node result = _nodeToAst[node];
     assert(result != null);
@@ -252,7 +259,7 @@ class KernelAstAdapter {
   ir.Procedure get mapLiteralConstructorEmpty =>
       kernel.functions[_backend.helpers.mapLiteralConstructorEmpty];
 
-  Element get jsIndexableLength => _backend.helpers.jsIndexableLength;
+  MemberElement get jsIndexableLength => _backend.helpers.jsIndexableLength;
 
   ir.Procedure get checkConcurrentModificationError =>
       kernel.functions[_backend.helpers.checkConcurrentModificationError];