Don't report an internal error if attempting to compile a file that doesn't exist.

dart/lib/compiler/implementation/dart2js.dart

 // Copyright (c) 2012, 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.
 
 #library('dart2js');
 
 #import('dart:io');
 #import('dart:uri');
 #import('dart:utf');
 
@@ skipping 91 matching lines @@
     helpAndFail('Error: Extra arguments: ${Strings.join(extra, " ")}');
   }
 
   Map<String, SourceFile> sourceFiles = <SourceFile>{};
   int dartBytesRead = 0;
 
   Future<String> provider(Uri uri) {
     if (uri.scheme != 'file') {
       throw new IllegalArgumentException(uri);
     }
-    String source = readAll(uriPathToNative(uri.path));
+    String source;
+    try {
+      source = readAll(uriPathToNative(uri.path));
+    } catch (FileIOException ex) {
+      throw 'Error: Cannot read "${relativize(cwd, uri)}" (${ex.osError}).';
+    }
     dartBytesRead += source.length;
     sourceFiles[uri.toString()] =
       new SourceFile(relativize(cwd, uri), source);
     Completer<String> completer = new Completer<String>();
     completer.complete(source);
     return completer.future;
   }
 
   void info(var message) {
     if (verbose) print('${colors.green("info:")} $message');
   }
 
+  bool isAborting = false;
+
   void handler(Uri uri, int begin, int end, String message, bool fatal) {
+    if (isAborting) return;
     if (uri === null && !fatal) {
       info(message);
       return;
     }
     if (uri === null) {
       assert(fatal);
       print(message);
     } else if (fatal || showWarnings) {
       SourceFile file = sourceFiles[uri.toString()];
       print(file.getLocationMessage(message, begin, end, true));
     }
-    if (fatal && throwOnError) throw new AbortLeg(message);
+    if (fatal && throwOnError) {
+      isAborting = true;
+      throw new AbortLeg(message);
+    }
   }
 
   Uri uri = cwd.resolve(arguments[0]);
   info('compiling $uri');
 
   // TODO(ahe): We expect the future to be complete and call value
   // directly. In effect, we don't support truly asynchronous API.
   String code = api.compile(uri, libraryRoot, provider, handler, options).value;
   if (code === null) {
     fail('Error: Compilation failed.');
@@ skipping 122 matching lines @@
     } catch (var ignored) {
       print('Internal error: error while printing exception');
     }
     try {
       print(trace);
     } finally {
       exit(253); // 253 is recognized as a crash by our test scripts.
     }
   }
 }