Use SummarySdkAnalysisContext if the SDK has the analysis_summary file.

pkg/analyzer/lib/src/generated/sdk_io.dart

Index: pkg/analyzer/lib/src/generated/sdk_io.dart
diff --git a/pkg/analyzer/lib/src/generated/sdk_io.dart b/pkg/analyzer/lib/src/generated/sdk_io.dart
index 1f98ba3eddfd7c26d85909f26e47e13cf530b73e..cf035d3badd92a522b9e015d96a0b53eed380592 100644
--- a/pkg/analyzer/lib/src/generated/sdk_io.dart
+++ b/pkg/analyzer/lib/src/generated/sdk_io.dart
@@ -18,6 +18,9 @@ import 'package:analyzer/src/generated/parser.dart';
 import 'package:analyzer/src/generated/scanner.dart';
 import 'package:analyzer/src/generated/sdk.dart';
 import 'package:analyzer/src/generated/source_io.dart';
+import 'package:analyzer/src/summary/format.dart' show SdkBundle;
+import 'package:analyzer/src/summary/summary_sdk.dart';
+import 'package:path/path.dart' as pathos;
 
 /**
  * A Dart SDK installed in a specified directory. Typical Dart SDK layout is
@@ -241,7 +244,12 @@ class DirectoryBasedDartSdk implements DartSdk {
   @override
   AnalysisContext get context {
     if (_analysisContext == null) {
-      _analysisContext = new SdkAnalysisContext();
+      SdkBundle sdkBundle = _getSummarySdkBundle();
+      if (sdkBundle != null) {
+        _analysisContext = new SummarySdkAnalysisContext(sdkBundle);
+      } else {
+        _analysisContext = new SdkAnalysisContext();
+      }
       SourceFactory factory = new SourceFactory([new DartUriResolver(this)]);
       _analysisContext.sourceFactory = factory;
       List<String> uris = this.uris;
@@ -533,6 +541,20 @@ class DirectoryBasedDartSdk implements DartSdk {
   }
 
   /**
+   * Return the [SdkBundle] for this SDK, if it exists, or `null` otherwise.
+   */
+  SdkBundle _getSummarySdkBundle() {
+    String rootPath = directory.getAbsolutePath();
+    String path = pathos.join(rootPath, 'lib', '_internal', 'analysis_summary');
+    File file = new File(path);
+    if (file.existsSync()) {

[Brian Wilkerson, 2016/01/05 18:46:18]

Should we catch IO exceptions here and return `null`, or do we want the
exception to propagate (and if the latter, how far)?

[Paul Berry, 2016/01/05 19:33:43]

I hope we can propagate (or at least report) the exception in such a way that if
it causes unit tests to fail, it will be obvious what has gone wrong.

Historically we have had enough defensive coding surrounding the code that
accesses core types in the SDK that when I've introduced a bug that interferes
with core types, the exception I got had no obvious relationship to the root
cause of the problem, and it was really difficult to figure out what I had done
wrong.  I'd like to avoid creating a similar situation here.

[scheglov, 2016/01/05 20:27:57]

I will catch all exceptions here and report them with
AnalysisEngine.instance.logger.logError().

+      List<int> bytes = file.readAsBytesSync();
+      return new SdkBundle.fromBuffer(bytes);
+    }
+    return null;
+  }
+
+  /**
    * Return the given [file] if it exists and is executable, or `null` if it
    * does not exist or is not executable.
    */