MB: Make Code Search builders use the phase configs.

The code search recipe passes --phase flag to the MB command
(see https://chromium-review.googlesource.com/c/505619/7)
so the MB config needs to be configured to support this.

BUG=chromium:699463
NOTRY=True

Review-Url: https://codereview.webrtc.org/2891583005
Cr-Commit-Position: refs/heads/master@{#18202}

tools_webrtc/mb/mb_config.pyl

@@ -108,8 +108,12 @@
       'Win64 Debug (Win10)': 'debug_bot_x64',
     },
     'chromium.infra.codesearch': {
-      'codesearch-gen-webrtc-android': 'android_debug_static_bot_arm',
-      'codesearch-gen-webrtc-linux': 'codesearch_gen_linux_bot',
+      'codesearch-gen-webrtc-android': {
+        'android': 'android_debug_static_bot_arm',
+      },
+      'codesearch-gen-webrtc-linux': {
+        'linux': 'codesearch_gen_linux_bot',
+      }
     },
     'tryserver.webrtc': {
       # iOS