Make CompilerTask independent of compiler.

pkg/compiler/lib/src/compile_time_constants.dart

Index: pkg/compiler/lib/src/compile_time_constants.dart
diff --git a/pkg/compiler/lib/src/compile_time_constants.dart b/pkg/compiler/lib/src/compile_time_constants.dart
index ed39469b41429260162a5e88bfe1ab3f68521f2f..9bab3a5f51368b109edcb5962d8032a682c56d44 100644
--- a/pkg/compiler/lib/src/compile_time_constants.dart
+++ b/pkg/compiler/lib/src/compile_time_constants.dart
@@ -6,7 +6,7 @@ library dart2js.compile_time_constant_evaluator;
 
 import 'common.dart';
 import 'common/resolution.dart' show Resolution;
-import 'common/tasks.dart' show CompilerTask;
+import 'common/tasks.dart' show CompilerTask, Measurer;
 import 'compiler.dart' show Compiler;
 import 'constant_system_dart.dart';
 import 'constants/constant_system.dart';
@@ -110,7 +110,7 @@ abstract class BackendConstantEnvironment extends ConstantEnvironment {
 /// frontend and backend interpretation of compile-time constants.
 abstract class ConstantCompilerTask extends CompilerTask
     implements ConstantCompiler {
-  ConstantCompilerTask(Compiler compiler) : super(compiler);
+  ConstantCompilerTask(Measurer measurer) : super(measurer);
 
   /// Copy all cached constant values from [task].
   ///