Compile JS with --minify.

CHANGELOG.md

@@ -3,6 +3,9 @@
 * Trust type annotations when compiling to JavaScript, which makes it
   substantially faster.
 
+* Compile to minified JavaScript, which decreases the code size substantially
+  and makes startup a little faster.
+
 ## 1.0.0-alpha.9
 
 * Elements without a namespace (such as `div`) are no longer unified with

tool/grind.dart

@@ -58,6 +58,7 @@ js() {
   _ensureBuild();
   var destination = new File('build/sass.dart.js');
   Dart2js.compile(new File('bin/sass.dart'), outFile: destination, extraArgs: [
+    '--minify',
     '--trust-type-annotations',
     '-Dnode=true',
     '-Dversion=$_version',