[rust] Fixing GN dependencies for test_cpp_including_rust_unittests.

`gn gen out/rust --check` detected some missing GN dependencies for
test_cpp_including_rust_unittests (i.e. including //base and
//base/allocator headers without explicitly covering these dependencies
in build/rust/tests/test_cpp_including_rust/BUILD.gn).  This CL adds
the missing dependencies.

Bug: 1069271
Change-Id: Ibd157412437e7d86bb856f081f9601078c29c20a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3180156
Auto-Submit: Łukasz Anforowicz <lukasza@chromium.org>
Reviewed-by: Adrian Taylor <adetaylor@chromium.org>
Commit-Queue: Łukasz Anforowicz <lukasza@chromium.org>
Cr-Commit-Position: refs/heads/main@{#924553}
diff --git a/build/rust/tests/test_cpp_including_rust/BUILD.gn b/build/rust/tests/test_cpp_including_rust/BUILD.gn
index ee34675..76e8446b 100644
--- a/build/rust/tests/test_cpp_including_rust/BUILD.gn
+++ b/build/rust/tests/test_cpp_including_rust/BUILD.gn
@@ -13,7 +13,8 @@
 test("test_cpp_including_rust_unittests") {
   sources = [ "unittests.cc" ]
   deps = [
-    "//base/allocator",
+    "//base",
+    "//base/allocator:buildflags",
     "//base/test:run_all_unittests",
     "//build/rust/tests/test_rust_source_set:test_rust_source_set_lib",
     "//testing/gmock",