Fix command line args validation for platform compilation with fasta

pkg/front_end/lib/src/fasta/compiler_command_line.dart

Index: pkg/front_end/lib/src/fasta/compiler_command_line.dart
diff --git a/pkg/front_end/lib/src/fasta/compiler_command_line.dart b/pkg/front_end/lib/src/fasta/compiler_command_line.dart
index 7788309d1c0e1e6e13308944709b0e9f35187375..96e59bb3519e81d4b821c964cd1fb3cc2705a8db 100644
--- a/pkg/front_end/lib/src/fasta/compiler_command_line.dart
+++ b/pkg/front_end/lib/src/fasta/compiler_command_line.dart
@@ -50,8 +50,8 @@ class CompilerCommandLine extends CommandLine {
     if (options.containsKey("-o") && options.containsKey("--output")) {
       return argumentError(usage, "Can't specify both '-o' and '--output'.");
     }
-    if (programName == "compile_platform" && arguments.length != 2) {
-      return argumentError(usage, "Expected two arguments.");
+    if (programName == "compile_platform" && arguments.length != 3) {
+      return argumentError(usage, "Expected three arguments.");
     } else if (arguments.isEmpty) {
       return argumentError(usage, "No Dart file specified.");
     }
@@ -121,7 +121,8 @@ String computeUsage(String programName, bool verbose) {
 
     case "compile_platform":
       summary = "Compiles Dart SDK platform to the Dill/Kernel IR format.";
-      basicUsage = "Usage: $programName [options] patched_sdk output\n";
+      basicUsage = "Usage: $programName [options] patched_sdk fullOutput "
+          "outlineOutput\n";
   }
   StringBuffer sb = new StringBuffer(basicUsage);
   if (summary != null) {