Use default bundle identifier for GPU process helper on macOS.

Chrome's and Chromium's helper bundle identifier is unfortunately
whitelisted by the OS, and renaming it breaks Chrome's use of
automatic graphics switching for OpenGL.

Tested in a Chromium build on a dual-GPU Mac and confirmed that this
change allows Chromium to release its hold on the discrete GPU ten
seconds after all WebGL contexts are released.

Bug: 985486
Change-Id: I87684230a6cc3f011c4d330ee1909e82dbc9f90c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1721830Reviewed-by: Mark Mentovai <mark@chromium.org>
Reviewed-by: Ken Rockot <rockot@google.com>
Commit-Queue: Kenneth Russell <kbr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#681541}

content/public/app/mac_helpers.gni

@@ -37,9 +37,12 @@ content_mac_helpers = [
 
   # A helper with the capability to execute writable memory, needed by
   # Swiftshader, and used to run renderer processes.
+  #
+  # Note: be careful if adding a suffix to this name - doing so may
+  # break automatic graphics switching. crbug.com/985486
   [
     "gpu",
-    ".gpu",
+    "",
     " (GPU)",
   ],