Reduce local resource fraciton for windows builds.

Reduces resources used for local compilation in racing for windows.
Makes machine running the build more responsive during the build.
Testing seems to show it doesn't impact overall build performance, and might even improve it slightly.

Bug: b/309819402
Change-Id: I6f4f41887b165c753508a57fcaa1a1a6931feee3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/5254559
Reviewed-by: Ben Segall <bentekkie@google.com>
Commit-Queue: Ben Segall <bentekkie@google.com>
Commit-Queue: Michael Savigny <msavigny@google.com>
Auto-Submit: Michael Savigny <msavigny@google.com>

reclient_helper.py

@@ -262,6 +262,10 @@ def set_win_defaults():
     # Enable the deps cache on windows.  This makes a notable improvement
     # in performance at the cost of a ~200MB cache file.
     os.environ.setdefault("RBE_enable_deps_cache", "true")
+    # Reduce local resource fraction used to do local compile actions on
+    # windows, to try and prevent machine saturation.
+    os.environ.setdefault("RBE_local_resource_fraction", "0.05")
+
 
 @contextlib.contextmanager
 def build_context(argv, tool):