Better error when force-compile fails

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

Index: pkg/dev_compiler/lib/src/compiler/command.dart
diff --git a/pkg/dev_compiler/lib/src/compiler/command.dart b/pkg/dev_compiler/lib/src/compiler/command.dart
index cd340db8154888a41ab01eb7940eb3a228509f73..af34e95f711c3490304d9cd70cff1f4cfdcaa5f6 100644
--- a/pkg/dev_compiler/lib/src/compiler/command.dart
+++ b/pkg/dev_compiler/lib/src/compiler/command.dart
@@ -186,7 +186,11 @@ void _compile(ArgResults argResults, AnalyzerOptions analyzerOptions,
   var module = compiler.compile(unit, compilerOpts);
   module.errors.forEach(printFn);
 
-  if (!module.isValid) throw new CompileErrorException();
+  if (!module.isValid) {
+    throw compilerOpts.unsafeForceCompile
+        ? new ForceCompileErrorException()
+        : new CompileErrorException();
+  }
 
   // Write JS file, as well as source map and summary (if requested).
   for (var i = 0; i < outPaths.length; i++) {
@@ -262,3 +266,9 @@ void _usageException(String message) {
 class CompileErrorException implements Exception {
   toString() => '\nPlease fix all errors before compiling (warnings are okay).';
 }
+
+/// Thrown when force compilation failed (probably due to static errors).
+class ForceCompileErrorException extends CompileErrorException {
+  toString() =>
+      '\nForce-compilation not successful. Please check static errors.';
+}