Use gclient's git_cache setting in bot_update/api.py

recipe_modules/gclient/config.py

Index: recipe_modules/gclient/config.py
diff --git a/recipe_modules/gclient/config.py b/recipe_modules/gclient/config.py
index b8152734b11bf7d14fdc6d71af65103a2719b4d7..ab17bc5fd43279ff61ff352e3c4e46a7401e11f1 100644
--- a/recipe_modules/gclient/config.py
+++ b/recipe_modules/gclient/config.py
@@ -14,7 +14,7 @@ def BaseConfig(USE_MIRROR=True, GIT_MODE=False, CACHE_DIR=None,
                PATCH_PROJECT=None, BUILDSPEC_VERSION=None,
                **_kwargs):
   deps = '.DEPS.git' if GIT_MODE else 'DEPS'
-  cache_dir = str(CACHE_DIR) if GIT_MODE and CACHE_DIR else None
+  cache_dir = str(CACHE_DIR) if GIT_MODE and CACHE_DIR else ''
   return ConfigGroup(
     solutions = ConfigList(
       lambda: ConfigGroup(
@@ -36,7 +36,8 @@ def BaseConfig(USE_MIRROR=True, GIT_MODE=False, CACHE_DIR=None,
     hooks = List(basestring),
     target_os = Set(basestring),
     target_os_only = Single(bool, empty_val=False, required=False),
-    cache_dir = Static(cache_dir, hidden=False),
+    cache_dir = Single(
+        basestring, empty_val=cache_dir, required=False, hidden=False),
 
     # If supplied, use this as the source root (instead of the first solution's
     # checkout).
@@ -169,6 +170,10 @@ def chromium(c):
   s.custom_deps = mirror_only(c, {})
 
 @config_ctx(includes=['chromium'])
+def chromium_no_git_cache(c):
+  c.cache_dir = ''
+
+@config_ctx(includes=['chromium'])
 def chromium_lkcr(c):
   # TODO(phajdan.jr): Add git hashes for LKCR crbug.com/349277.
   if c.GIT_MODE: