Fix duplicate shim symbols in chromium build

Bug: pdfium:2038
Change-Id: I6f6e3985fe03aef598e3c8d90330b6253f438a66
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/107731
Commit-Queue: Tom Sepez <tsepez@chromium.org>
Reviewed-by: Lei Zhang <thestig@chromium.org>
diff --git a/testing/BUILD.gn b/testing/BUILD.gn
index 1d1fc59..22e64a4 100644
--- a/testing/BUILD.gn
+++ b/testing/BUILD.gn
@@ -3,6 +3,7 @@
 # found in the LICENSE file.
 
 import("//build/config/sanitizers/sanitizers.gni")
+import("//build_overrides/build.gni")
 import("../pdfium.gni")
 
 source_set("test_support") {
@@ -50,7 +51,8 @@
     "../:pdfium_noshorten_config",
   ]
   visibility = [ "../*" ]
-  if (pdf_use_partition_alloc && !is_win && !is_asan && !is_msan && !is_ubsan) {
+  if (pdf_use_partition_alloc && !build_with_chromium && !is_win && !is_asan &&
+      !is_msan && !is_ubsan) {
     sources += [ "utils/malloc_shim.cpp" ]
     deps += [ "//base/allocator/partition_allocator:partition_alloc" ]
   }