Split the Kernel transformations into modular and global ones

pkg/kernel/lib/target/targets.dart

 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 library kernel.target.targets;
 
 import '../ast.dart';
 
 import 'vm.dart';
 import 'vmcc.dart';
 import 'flutter.dart';
@@ skipping 34 matching lines @@
   /// These can also be passed on the command-line of form `-D<name>=<value>`,
   /// and those provided on the command-line take precedence over those defined
   /// by the target.
   Map<String, String> get extraDeclaredVariables => const <String, String>{};
 
   bool get strongMode;
 
   /// If true, the SDK should be loaded in strong mode.
   bool get strongModeSdk => strongMode;
 
-  void transformProgram(Program program);
+  /// Perform target-specific modular transformations.
+  ///
+  /// These transformations should not be whole-program transformations.  They
+  /// should expect that the program will contain external libraries.
+  void performModularTransformations(Program program);
+
+  /// Perform target-specific whole-program transformations.
+  ///
+  /// These transformations should be optimizations and not required for
+  /// correctness.  Everything should work if a simple and fast linker chooses
+  /// not to apply these transformations.
+  void performGlobalTransformations(Program program);
 
   String toString() => 'Target($name)';
 }
 
 class NoneTarget extends Target {
   final TargetFlags flags;
 
   NoneTarget(this.flags);
 
   bool get strongMode => flags.strongMode;
   String get name => 'none';
   List<String> get extraRequiredLibraries => <String>[];
-  void transformProgram(Program program) {}
+  void performModularTransformations(Program program) {}
+  void performGlobalTransformations(Program program) {}
 }