allocator: rename use_experimental_allocator_shim to use_allocator_shim

This is a pure buildflag renaming with no intended functional changes.
The allocator shim has been stably shipped to various stable versions
on Windows, Linux, Android, CrOS and Mac OS, hence is not experimental
anymore.

BUG=550886
TBR=rockot

Review-Url: https://codereview.chromium.org/2902043007
Cr-Original-Commit-Position: refs/heads/master@{#474655}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 73228cd43d2e9794bab5a8508c5db4b23704bc84
diff --git a/tools/gn/bootstrap/bootstrap.py b/tools/gn/bootstrap/bootstrap.py
index c52779e..6f2f5b1 100755
--- a/tools/gn/bootstrap/bootstrap.py
+++ b/tools/gn/bootstrap/bootstrap.py
@@ -167,7 +167,7 @@
   mkdir_p(root_gen_dir)
 
   write_buildflag_header_manually(root_gen_dir, 'base/allocator/features.h',
-      {'USE_EXPERIMENTAL_ALLOCATOR_SHIM': 'true' if is_linux else 'false'})
+      {'USE_ALLOCATOR_SHIM': 'true' if is_linux else 'false'})
 
   write_buildflag_header_manually(root_gen_dir, 'base/debug/debugging_flags.h',
       {