Edit Brotli BUILD.gn to make fuzzers optional

Embedders of Brotli from chromium's dependencies (ex: PDFium) do not
need the fuzzers and usually do not include libfuzzer when standalone,
hence this CL uses the build_with_chromium argument for these embedders
so that the fuzzers do not need to be built and the additional
dependency does not need to be pulled for the standalone repo.

Bug: 475855993
Change-Id: Ia63de8690f5cc053305afb07701abdf52d2dd300
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/7882000
Reviewed-by: Kenichi Ishibashi <bashi@chromium.org>
Reviewed-by: Lei Zhang <thestig@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1638220}
NOKEYCHECK=True
GitOrigin-RevId: 0f3cbd59af8502ab127acd8dd8fa950fed90d550

BUILD.gn

diff --git a/BUILD.gn b/BUILD.gn
index bcc500d..0a9eb55 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -2,7 +2,11 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-import("//testing/libfuzzer/fuzzer_test.gni")
+import("//build/config/gclient_args.gni")
+
+if (build_with_chromium) {
+  import("//testing/libfuzzer/fuzzer_test.gni")
+}
 
 if (is_win) {
   import("//build/config/win/visual_studio_version.gni")
@@ -227,8 +231,10 @@
   }
 }
 
-fuzzer_test("brotli_fuzzer") {
-  sources = [ "fuzz/decode_fuzzer.c" ]
-  deps = [ ":dec" ]
-  libfuzzer_options = [ "max_len=1280" ]
+if (build_with_chromium) {
+  fuzzer_test("brotli_fuzzer") {
+    sources = [ "fuzz/decode_fuzzer.c" ]
+    deps = [ ":dec" ]
+    libfuzzer_options = [ "max_len=1280" ]
+  }
 }