Add support for SDK outline in IKG.

pkg/front_end/lib/src/base/processed_options.dart

 // Copyright (c) 2017, 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 'dart:async';
 
 import 'package:front_end/compilation_message.dart';
 import 'package:front_end/compiler_options.dart';
 import 'package:front_end/file_system.dart';
 import 'package:front_end/src/base/performace_logger.dart';
@@ skipping 71 matching lines @@
     _ensureSdkDefaults();
     return _sdkRoot;
   }
 
   Uri _sdkSummary;
   Uri get sdkSummary {
     _ensureSdkDefaults();
     return _sdkSummary;
   }
 
+  List<int> _sdkSummaryBytes;
+
+  /// Get the bytes of the SDK outline, if any.
+  Future<List<int>> loadSdkSummaryBytes() async {
+    if (_sdkSummaryBytes == null) {
+      if (sdkSummary == null) return null;
+      var entry = fileSystem.entityForUri(sdkSummary);
+      _sdkSummaryBytes = await entry.readAsBytes();
+    }
+    return _sdkSummaryBytes;
+  }
+
   Uri _librariesSpecificationUri;
   Uri get librariesSpecificationUri {
     _ensureSdkDefaults();
     return _librariesSpecificationUri;
   }
 
   Ticker ticker;
 
   bool get verbose => _raw.verbose;
 
@@ skipping 131 matching lines @@
 
   Target _target;
   Target get target => _target ??=
       _raw.target ?? new VmFastaTarget(new TargetFlags(strongMode: strongMode));
 
   /// Get an outline program that summarizes the SDK, if any.
   // TODO(sigmund): move, this doesn't feel like an "option".
   Future<Program> loadSdkSummary(CanonicalName nameRoot) async {
     if (_sdkSummaryProgram == null) {
       if (sdkSummary == null) return null;
-      var bytes = await fileSystem.entityForUri(sdkSummary).readAsBytes();
+      var bytes = await loadSdkSummaryBytes();
       _sdkSummaryProgram = loadProgram(bytes, nameRoot);
     }
     return _sdkSummaryProgram;
   }
 
   /// Get the summary programs for each of the underlying `inputSummaries`
   /// provided via [CompilerOptions].
   // TODO(sigmund): move, this doesn't feel like an "option".
   Future<List<Program>> loadInputSummaries(CanonicalName nameRoot) async {
     if (_inputSummariesPrograms == null) {
@@ skipping 348 matching lines @@
   String get dart2jsCode => _original.code.dart2jsCode;
 
   SourceSpan get span =>
       new SourceLocation(_original.charOffset, sourceUrl: _original.uri)
           .pointSpan();
 
   _CompilationMessage(this._original, this.severity);
 
   String toString() => message;
 }