Add a cast audio bot.

tools/mb/mb_config.pyl

Index: tools/mb/mb_config.pyl
diff --git a/tools/mb/mb_config.pyl b/tools/mb/mb_config.pyl
index a74172d27d9bd27c16baee8a45f502a0f9239f62..43cdc0afff28665cba5e10c1681cb2ff815b46c2 100644
--- a/tools/mb/mb_config.pyl
+++ b/tools/mb/mb_config.pyl
@@ -266,6 +266,7 @@
       'Android Tests': 'android_release_bot_minimal_symbols',
       'Cast Android (dbg)': 'android_cast_debug_static_bot',
       'Cast Linux': 'cast_release_bot',
+      'Cast Audio Linux': 'cast_audio_release_bot',
       'Linux Builder (dbg)': 'debug_bot',
       'Linux Builder (dbg)(32)': 'debug_bot_x86',
       'Linux Builder': 'release_bot',
@@ -538,6 +539,7 @@
       'Chromium Linux Codesearch Builder': 'codesearch',
       'ChromiumOS Codesearch Builder': 'codesearch',
       'cast_shell_linux': 'cast_release_trybot',
+      'cast_shell_audio_linux': 'cast_audio_release_trybot',
       'chromeos_amd64-generic_chromium_compile_only_ng': 'cros_chrome_sdk',
       'chromeos_daisy_chromium_compile_only_ng': 'cros_chrome_sdk',
       'chromeos_x86-generic_chromium_compile_only_ng': 'cros_chrome_sdk',
@@ -981,6 +983,14 @@
       'cast', 'release_trybot',
     ],
 
+    'cast_audio_release_bot': [
+      'cast', 'cast_audio', 'release_bot',
+    ],
+
+    'cast_audio_release_trybot': [
+      'cast', 'cast_audio', 'release_trybot',
+    ],
+
     'cfi_full_cfi_diag_release_static': [
       'cfi_full', 'cfi_diag', 'release', 'static',
     ],
@@ -1577,6 +1587,10 @@
       'gn_args': 'is_chromecast=true',
     },
 
+    'cast_audio': {
+      'gn_args': 'is_cast_audio_only=true enable_webrtc=false'
+    },
+
     'cfi': {
       'gn_args': 'is_cfi=true',
     },