Rename apiimpl.Compiler to CompilerImpl.

tests/compiler/dart2js/bad_loop_test.dart

 // Copyright (c) 2013, 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.
 
 import 'package:expect/expect.dart';
 import 'memory_source_file_helper.dart';
 import "package:async_helper/async_helper.dart";
 
 import 'package:compiler/compiler.dart'
        show Diagnostic;
@@ skipping 15 matching lines @@
     }
     if (kind == Diagnostic.ERROR) {
       errorCount++;
     } else if (kind == Diagnostic.WARNING) {
       warningCount++;
     } else {
       throw 'unexpected diagnostic $kind: $message';
     }
   }
 
-  Compiler compiler = new Compiler(
+  CompilerImpl compiler = new CompilerImpl(
       new LegacyCompilerInput(provider.readStringFromUri),
       new LegacyCompilerOutput(),
       new LegacyCompilerDiagnostics(diagnosticHandler),
       libraryRoot,
       packageRoot,
       [Flags.analyzeOnly],
       {});
   asyncTest(() => compiler.run(Uri.parse('memory:main.dart')).then((_) {
     Expect.isTrue(compiler.compilationFailed);
     Expect.equals(5, errorCount);
@@ skipping 14 matching lines @@
   }
 
   for ((){}() in []) {
   }
 
   for (1 in []) {
   }
 }
 """
 };