Before:
```
dart compile js --wrong-flag
Compile Dart to JavaScript.
Usage: dart compile js [arguments] <dart entry point>
-h, --help Print this usage information.
-h -v Show detailed information about all options.
-o, --output Write the output to <file name>.
-O<0,1,2,3,4> Set the compiler optimization level (defaults to -O1).
-O0 No optimizations (only meant for debugging the compiler).
-O1 Default (includes whole program analyses and inlining).
-O2 Safe production-oriented optimizations (like minification).
-O3 Potentially unsafe optimizations (see -h -v for details).
-O4 More agressive unsafe optimizations (see -h -v for details).
<-- TWO SPACES HERE and a newline
Error: Unknown option '--wrong-flag'.
```
After this change:
```
dart compile js --wrong-flag
Compile Dart to JavaScript.
Usage: dart compile js [arguments] <dart entry point>
-h, --help Print this usage information.
-h -v Show detailed information about all options.
-o, --output Write the output to <file name>.
-O<0,1,2,3,4> Set the compiler optimization level (defaults to -O1).
-O0 No optimizations (only meant for debugging the compiler).
-O1 Default (includes whole program analyses and inlining).
-O2 Safe production-oriented optimizations (like minification).
-O3 Potentially unsafe optimizations (see -h -v for details).
-O4 More agressive unsafe optimizations (see -h -v for details).
Error: Unknown option '--wrong-flag'.
```
R=sra@google.com
Change-Id: Ie0541d830b53e3e81b4b02a20988cbd41db64325
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/339300
Auto-Submit: Morgan :) <davidmorgan@google.com>
Reviewed-by: Stephen Adams <sra@google.com>
Commit-Queue: Morgan :) <davidmorgan@google.com>
David Morgan
29268c6c1d