Revert "Revert "Report error if the same uri appears in multiple summaries.""

pkg/analyzer_cli/lib/src/build_mode.dart

Index: pkg/analyzer_cli/lib/src/build_mode.dart
diff --git a/pkg/analyzer_cli/lib/src/build_mode.dart b/pkg/analyzer_cli/lib/src/build_mode.dart
index 0fa7fa6d64e65beeb5cc8eeb0878d222d52d738b..985511db795d58c303585312c7a6a99c3d020c48 100644
--- a/pkg/analyzer_cli/lib/src/build_mode.dart
+++ b/pkg/analyzer_cli/lib/src/build_mode.dart
@@ -169,7 +169,13 @@ class BuildMode {
         .toList());
 
     // Prepare the analysis context.
-    _createContext();
+    try {
+      _createContext();
+    } on ConflictingSummaryException catch (e) {
+      errorSink.writeln('$e');
+      io.exitCode = ErrorSeverity.ERROR.ordinal;
+      return ErrorSeverity.ERROR;
+    }
 
     // Add sources.
     ChangeSet changeSet = new ChangeSet();