Address more TODO(GYP) in the GN build.

components/crash/content/app/BUILD.gn

Index: components/crash/content/app/BUILD.gn
diff --git a/components/crash/content/app/BUILD.gn b/components/crash/content/app/BUILD.gn
index 8d871fe8b6572eea1a72a08d3bdab496012805c5..ba1f3a51940a021c039f2771bcf7a37fff858f40 100644
--- a/components/crash/content/app/BUILD.gn
+++ b/components/crash/content/app/BUILD.gn
@@ -187,3 +187,34 @@ source_set("app_breakpad_mac_win_to_be_deleted") {
     }
   }
 }
+
+if (is_mac) {
+  source_set("breakpad_stubs") {
+    sources = [
+      "breakpad_mac.h",
+      "breakpad_mac_stubs.mm",
+      "crash_reporter_client.cc",
+      "crash_reporter_client.h",
+    ]
+    deps = [
+      "//base",
+    ]
+  }
+}
+
+source_set("unit_tests") {
+  testonly = true
+  sources = [
+    "crash_keys_win_unittest.cc",
+  ]
+  deps = [
+    ":lib",
+    "//base",
+    "//testing/gmock",
+    "//testing/gtest",
+  ]
+
+  if (is_win) {
+    deps += [ "//breakpad:client" ]
+  }
+}