Report error if the same uri appears in multiple summaries.

pkg/dev_compiler/lib/src/compiler/command.dart

 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 import 'dart:io';
 import 'package:analyzer/src/command_line/arguments.dart'
     show
         defineAnalysisArguments,
         filterUnknownArguments,
         ignoreUnrecognizedFlagsFlag;
 import 'package:analyzer/src/generated/source.dart' show Source;
 import 'package:analyzer/src/summary/package_bundle_reader.dart'
-    show InSummarySource;
+    show ConflictingSummaryException, InSummarySource;
 import 'package:args/args.dart' show ArgParser, ArgResults;
 import 'package:args/command_runner.dart' show UsageException;
 import 'package:path/path.dart' as path;
 
 import '../analyzer/context.dart' show AnalyzerOptions;
 import 'compiler.dart' show BuildUnit, CompilerOptions, ModuleCompiler;
 import 'module_builder.dart';
 
 const _binaryName = 'dartdevc';
 
@@ skipping 32 matching lines @@
     return 0;
   }
 
   try {
     _compile(argResults, analyzerOptions, printFn);
     return 0;
   } on UsageException catch (error) {
     // Incorrect usage, input file not found, etc.
     printFn(error);
     return 64;
+  } on ConflictingSummaryException catch (error) {
+    // Same input file appears in multiple provided summaries.
+    printFn(error);
+    return 65;
   } on CompileErrorException catch (error) {
     // Code has error(s) and failed to compile.
     printFn(error);
     return 1;
   } catch (error, stackTrace) {
     // Anything else is likely a compiler bug.
     //
     // --unsafe-force-compile is a bit of a grey area, but it's nice not to
     // crash while compiling
     // (of course, output code may crash, if it had errors).
@@ skipping 174 matching lines @@
 }
 
 void _usageException(String message) {
   throw new UsageException(message, _usageMessage);
 }
 
 /// Thrown when the input source code has errors.
 class CompileErrorException implements Exception {
   toString() => '\nPlease fix all errors before compiling (warnings are okay).';
 }