Implement modular compilation

lib/src/compiler/nullable_type_inference.dart

Index: lib/src/compiler/nullable_type_inference.dart
diff --git a/lib/src/codegen/nullable_type_inference.dart b/lib/src/compiler/nullable_type_inference.dart
similarity index 97%
rename from lib/src/codegen/nullable_type_inference.dart
rename to lib/src/compiler/nullable_type_inference.dart
index 562d63d7885ae2b07ca7f55faee12b768adf0691..f930333ed6fd3dbde59e14def4febf222b65e664 100644
--- a/lib/src/codegen/nullable_type_inference.dart
+++ b/lib/src/compiler/nullable_type_inference.dart
@@ -8,7 +8,7 @@ import 'package:analyzer/dart/ast/token.dart' show TokenType;
 import 'package:analyzer/dart/ast/visitor.dart' show RecursiveAstVisitor;
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/dart/element/type.dart';
-import '../utils.dart' show getStaticType, isInlineJS;
+import 'element_helpers.dart' show getStaticType, isInlineJS;
 
 /// An inference engine for nullable types.
 ///
@@ -21,15 +21,16 @@ import '../utils.dart' show getStaticType, isInlineJS;
 // TODO(vsm): Revisit whether we really need this when we get
 // better non-nullability in the type system.
 abstract class NullableTypeInference {
+  LibraryElement dartCoreLibrary;
   bool isPrimitiveType(DartType type);
   bool isObjectProperty(String name);
 
   /// Known non-null local variables.
   HashSet<LocalVariableElement> _notNullLocals;
 
-  void inferNullableTypesInLibrary(Iterable<CompilationUnit> units) {
+  void inferNullableTypes(AstNode node) {
     var visitor = new _NullableLocalInference(this);
-    for (var unit in units) unit.accept(visitor);
+    node.accept(visitor);
     _notNullLocals = visitor.computeNotNullLocals();
   }
 
@@ -178,9 +179,7 @@ abstract class NullableTypeInference {
         }
       }
 
-      if (e != null &&
-          e.name == 'identical' &&
-          e.library.source.uri.toString() == 'dart:core') {
+      if (e?.name == 'identical' && identical(e.library, dartCoreLibrary)) {
         return false;
       }
     }