Add placeholder to insert sign-in token for testing

A subsequent test will reference this new #define.
Manually adding this define will override the bearer
authorization token used in requests, so that we can
simulate a signed-in account when running a test.

Bug: 1141619
Change-Id: I4fb34af8367a91fb09a7f2b8096aec94094d9bb6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2518278Reviewed-by: Carlos Knippschild <carlosk@chromium.org>
Commit-Queue: Dan H <harringtond@chromium.org>
Cr-Commit-Position: refs/heads/master@{#824493}

components/feed/core/v2/feed_network_impl.cc

@@ -12,6 +12,7 @@
 #include "base/containers/flat_set.h"
 #include "base/metrics/histogram_functions.h"
 #include "base/metrics/histogram_macros.h"
+#include "base/strings/strcat.h"
 #include "base/time/tick_clock.h"
 #include "base/time/time.h"
 #include "components/feed/core/common/pref_names.h"
@@ -39,6 +40,9 @@
 #include "third_party/protobuf/src/google/protobuf/io/coded_stream.h"
 #include "third_party/zlib/google/compression_utils.h"
 
+// Token override for Feedv2NewTabPageCardInstrumentationTest.java:
+// #define TOKEN_OVERRIDE_FOR_TESTING  "put-test-token-here"
+
 namespace feed {
 namespace {
 constexpr char kApplicationXProtobuf[] = "application/x-protobuf";
@@ -312,8 +316,12 @@ class FeedNetworkImpl::NetworkFetch {
 
     variations::SignedIn signed_in_status = variations::SignedIn::kNo;
     if (!access_token_.empty()) {
+      base::StringPiece token = access_token_;
+#ifdef TOKEN_OVERRIDE_FOR_TESTING
+      token = TOKEN_OVERRIDE_FOR_TESTING;
+#endif
       request.headers.SetHeader(net::HttpRequestHeaders::kAuthorization,
-                                "Bearer " + access_token_);
+                                base::StrCat({"Bearer ", token}));
       signed_in_status = variations::SignedIn::kYes;
     }