Support multiple resolution inputs from command line.

pkg/compiler/lib/src/diagnostics/messages.dart

Index: pkg/compiler/lib/src/diagnostics/messages.dart
diff --git a/pkg/compiler/lib/src/diagnostics/messages.dart b/pkg/compiler/lib/src/diagnostics/messages.dart
index 830a010ad396a68d44db01c3a90f7fa02f092978..500b6c451bf9490ad1a6a1d2b61fbf38aaa3c003 100644
--- a/pkg/compiler/lib/src/diagnostics/messages.dart
+++ b/pkg/compiler/lib/src/diagnostics/messages.dart
@@ -177,6 +177,7 @@ enum MessageKind {
   DUPLICATE_IMPORT,
   DUPLICATE_INITIALIZER,
   DUPLICATE_LABEL,
+  DUPLICATE_SERIALIZED_LIBRARY,
   DUPLICATE_SUPER_INITIALIZER,
   DUPLICATE_TYPE_VARIABLE_NAME,
   DUPLICATED_LIBRARY_NAME,
@@ -3676,6 +3677,11 @@ $MIRRORS_NOT_SUPPORTED_BY_BACKEND_PADDING#{importChain}"""),
           MessageKind.UNRECOGNIZED_VERSION_OF_LOOKUP_MAP,
           "Unsupported version of package:lookup_map.",
           howToFix: DONT_KNOW_HOW_TO_FIX),
+
+      MessageKind.DUPLICATE_SERIALIZED_LIBRARY: const MessageTemplate(
+          MessageKind.DUPLICATE_SERIALIZED_LIBRARY,
+          "Library '#{libraryUri}' found in both '#{sourceUri1}' and "
+          "'#{sourceUri2}'."),
     }); // End of TEMPLATES.
 
   /// Padding used before and between import chains in the message for