[Android] Switch the x86, x64, and mips builders on chromium.android to mb.

scripts/slave/recipe_modules/chromium_android/config.py

Index: scripts/slave/recipe_modules/chromium_android/config.py
diff --git a/scripts/slave/recipe_modules/chromium_android/config.py b/scripts/slave/recipe_modules/chromium_android/config.py
index 4580b659086772fcf7d7e523e2600800ee634df4..c0108634939aea00fea13accd09e5dff6001ee0b 100644
--- a/scripts/slave/recipe_modules/chromium_android/config.py
+++ b/scripts/slave/recipe_modules/chromium_android/config.py
@@ -84,6 +84,10 @@ def x86_base(c):
 def x86_builder(c):
   pass
 
+@config_ctx(includes=['x86_builder'])
+def x86_builder_mb(c):
+  pass
+
 @config_ctx()
 def mipsel_base(c):
   pass
@@ -92,6 +96,10 @@ def mipsel_base(c):
 def mipsel_builder(c):
   pass
 
+@config_ctx(includes=['mipsel_base'])
+def mipsel_builder_mb(c):
+  pass
+
 @config_ctx(includes=['main_builder'])
 def dartium_builder(c):  # pragma: no cover
   c.get_app_manifest_vars = False
@@ -119,7 +127,7 @@ def x64_base(c):
   pass
 
 @config_ctx(includes=['x64_base'])
-def x64_builder(c):
+def x64_builder_mb(c):
   pass
 
 @config_ctx()