Turn on SDK summaries in flutter analyze.

The latest dev build has stable summaries so we should start using them.

(Also ensures that analysis options are propogating to the SDK analysis context --- see:  https://github.com/dart-lang/sdk/issues/26129.)

packages/flutter_tools/lib/src/dart/analysis.dart

@@ -91,7 +91,9 @@ class AnalysisDriver {
 
   List<UriResolver> _getResolvers(InternalAnalysisContext context,
       Map<String, List<file_system.Folder>> packageMap) {
-    DartSdk sdk = new DirectoryBasedDartSdk(new JavaFile(sdkDir));
+    DirectoryBasedDartSdk sdk = new DirectoryBasedDartSdk(new JavaFile(sdkDir));
+    sdk.analysisOptions = context.analysisOptions;
+    sdk.useSummary = true;
     List<UriResolver> resolvers = <UriResolver>[];
 
     EmbedderYamlLocator yamlLocator = context.embedderYamlLocator;