Enable deps cache for mac devs.

Turns on deps cache, and increases it's size, for mac developers.  In
some cases, it shows good improvements on chrome builds (cutting 1-4
minutes off a full chrome build, once populated).

Bug: b/322801289
Change-Id: I9cd2b35b5429228c07b0703d6c3344963e4fb9e5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/5258563
Auto-Submit: Michael Savigny <msavigny@google.com>
Reviewed-by: Ben Segall <bentekkie@google.com>
Commit-Queue: Michael Savigny <msavigny@google.com>

reclient_helper.py

@@ -256,6 +256,10 @@ def set_mac_defaults():
     # performance when on high-speed connection, but does show improvements
     # on easily congested networks.
     os.environ.setdefault("RBE_cas_concurrency", "100")
+    # Enable the deps cache on macs.  Mac needs a larger deps cache as it
+    # seems to have larger dependency sets per action.
+    os.environ.setdefault("RBE_enable_deps_cache", "true")
+    os.environ.setdefault("RBE_deps_cache_max_mb", "1024")
 
 
 def set_win_defaults():