Conditionally enable SDK summaries in server

pkg/analysis_server/lib/src/server/driver.dart

Index: pkg/analysis_server/lib/src/server/driver.dart
diff --git a/pkg/analysis_server/lib/src/server/driver.dart b/pkg/analysis_server/lib/src/server/driver.dart
index ae8c50f43b62d44c874e0e92cb7d644a3a3d5b90..d70517b8af6f8a6f94154884799a81bd2b6fe5e1 100644
--- a/pkg/analysis_server/lib/src/server/driver.dart
+++ b/pkg/analysis_server/lib/src/server/driver.dart
@@ -407,10 +407,12 @@ class Driver implements ServerStarter {
       // Use DirectoryBasedDartSdk.defaultSdkDirectory, which will make a guess.
       defaultSdkDirectory = DirectoryBasedDartSdk.defaultSdkDirectory;
     }
+    bool useSummaries = analysisServerOptions.fileReadMode == 'as-is';
     SdkCreator defaultSdkCreator = (AnalysisOptions options) {
       DirectoryBasedDartSdk sdk =
           new DirectoryBasedDartSdk(defaultSdkDirectory);
       sdk.analysisOptions = options;
+      sdk.useSummary = useSummaries;
       return sdk;
     };
     // TODO(brianwilkerson) It would be nice to avoid creating an SDK that