Extract DiagnosticReporter implementation from Compiler.

pkg/compiler/lib/src/common/tasks.dart

Index: pkg/compiler/lib/src/common/tasks.dart
diff --git a/pkg/compiler/lib/src/common/tasks.dart b/pkg/compiler/lib/src/common/tasks.dart
index 32966df50b3fbdd936ed8d9df26cd518ff3eba15..56253dbf3cbdafb28eb49945fac5b21f21bb1b25 100644
--- a/pkg/compiler/lib/src/common/tasks.dart
+++ b/pkg/compiler/lib/src/common/tasks.dart
@@ -8,6 +8,8 @@ import 'dart:profiler' show
     UserTag;
 import '../compiler.dart' show
     Compiler;
+import '../diagnostics/diagnostic_listener.dart' show
+    DiagnosticReporter;
 import '../elements/elements.dart' show
     Element;
 
@@ -30,6 +32,8 @@ class CompilerTask {
       : this.compiler = compiler,
         watch = (compiler.verbose) ? new Stopwatch() : null;
 
+  DiagnosticReporter get reporter => compiler.reporter;
+
   String get name => "Unknown task '${this.runtimeType}'";
 
   int get timing {
@@ -66,7 +70,7 @@ class CompilerTask {
   }
 
   measureElement(Element element, action()) {
-    compiler.withCurrentElement(element, () => measure(action));
+    reporter.withCurrentElement(element, () => measure(action));
   }
 
   /// Measure the time spent in [action] (if in verbose mode) and accumulate it