support ui_mode cli flag for start command

Author: petemill

lib/start.js

@@ -19,6 +19,9 @@ const start = (buildConfig = config.defaultBuildConfig, options) => {
   if (options.disable_pdfjs_extension) {
     braveArgs.push('--disable-pdfjs-extension')
   }
+  if (options.ui_mode) {
+    braveArgs.push(`--ui-mode=${options.ui_mode}`)
+  }
   if (!options.enable_brave_update) {
     // This only has meaning with MacOS and official build.
     braveArgs.push('--disable-brave-update')

scripts/commands.js

@@ -67,6 +67,7 @@ program
   .option('--no_sandbox', 'disable the sandbox')
   .option('--disable_brave_extension', 'disable loading the Brave extension')
   .option('--disable_pdfjs_extension', 'disable loading the PDFJS extension')
+  .option('--ui_mode <ui_mode>', 'which built-in ui appearance mode to use', /^(dark|light)$/i)
   .option('--enable_brave_update', 'enable brave update')
   .option('--channel <target_chanel>', 'target channel to start', /^(beta|dev|nightly|release)$/i, 'release')
   .option('--official_build <official_build>', 'force official build settings')