Flag --with-dartium should install dartium

tools/apps/update_homebrew/bin/update_homebrew.dart

Index: tools/apps/update_homebrew/bin/update_homebrew.dart
diff --git a/tools/apps/update_homebrew/bin/update_homebrew.dart b/tools/apps/update_homebrew/bin/update_homebrew.dart
index a1e458619ab40ccf20bfe64c01024dcedcb53d6f..d87631a6884c6c931d99111e256f68fee84b69ec 100644
--- a/tools/apps/update_homebrew/bin/update_homebrew.dart
+++ b/tools/apps/update_homebrew/bin/update_homebrew.dart
@@ -227,21 +227,21 @@ class Dart < Formula
     version '$stableVersion'
     url '$urlBase/stable/release/${revisions['stable']}/$dartiumFile'
     sha256 '${hashes['stable'][dartiumFile]}'
   end
 
   def install
     libexec.install Dir['*']
     bin.install_symlink "#{libexec}/bin/dart"
     bin.write_exec_script Dir["#{libexec}/bin/{pub,docgen,dart?*}"]
 
-    if build.with? 'content-shell'
+    if build.with? 'dartium'
       dartium_binary = 'Chromium.app/Contents/MacOS/Chromium'
       prefix.install resource('dartium')
       (bin+"dartium").write shim_script dartium_binary
     end
 
     if build.with? 'content-shell'
       content_shell_binary = 'Content Shell.app/Contents/MacOS/Content Shell'
       prefix.install resource('content_shell')
       (bin+"content_shell").write shim_script content_shell_binary
     end
@@ -253,21 +253,21 @@ class Dart < Formula
       exec "#{prefix}/#{target}" "\$@"
     EOS
   end
 
   def caveats; <<-EOS.undent
     Please note the path to the Dart SDK:
       #{opt_libexec}
 
     --with-dartium:
       To use with IntelliJ, set the Dartium execute home to:
-        #{prefix}/Chromium.app
+        #{opt_prefix}/Chromium.app
     EOS
   end
 
   test do
     (testpath/'sample.dart').write <<-EOS.undent
       void main() {
         print(r"test message");
       }
     EOS