Use messages for (some) public API errors

pkg/front_end/messages.yaml

 # Copyright (c) 2017, 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.
 
 # Each entry in this map corresponds to a diagnostic message. Ideally, each
 # entry contains three parts:
 #
 # 1. A message template (template).
 #
 # 2. A suggestion for how to correct the problem (tip).
@@ skipping 531 matching lines @@
       --fatal=errors
       --fatal=warnings
       --fatal=nits
         Makes messages of the given kinds fatal, that is, immediately stop the
         compiler with a non-zero exit-code. In --verbose mode, also display an
         internal stack trace from the compiler. Multiple kinds can be separated by
         commas, for example, --fatal=errors,warnings.
 
 FastaCLIArgumentRequired:
   template: "Expected value after '#name'."
+
+MissingMain:
+  template: "No 'main' method found."
+  tip: "Try adding a method named 'main' to your program."
+  dart2jsCode: MISSING_MAIN
+
+MissingInputFile:
+  template: "Input file not found: #string."
+
+MissingSdkRoot:
+  template: "SDK root directory not found: #string."
+
+MissingSdkSummary:
+  template: "SDK summary not found: #string."
+
+CombinedCompileSdkAndSummary:
+  template: "The compileSdk and sdkSummary options are mutually exclusive"
+
+VerificationError:
+  template: "An internal error was found while verifying the output of the compiler. #string"