Refactor webrtc_perf_tests into several source_sets.

webrtc/modules/remote_bitrate_estimator/BUILD.gn

Index: webrtc/modules/remote_bitrate_estimator/BUILD.gn
diff --git a/webrtc/modules/remote_bitrate_estimator/BUILD.gn b/webrtc/modules/remote_bitrate_estimator/BUILD.gn
index f73fa22067389f6ea74172a9877b319b08ae95b4..ff8c27cdc4ced62d28450d8fb70afcdb71ba4b7d 100644
--- a/webrtc/modules/remote_bitrate_estimator/BUILD.gn
+++ b/webrtc/modules/remote_bitrate_estimator/BUILD.gn
@@ -124,4 +124,18 @@ if (rtc_include_tests) {
       "//testing/gtest",
     ]
   }
+
+  rtc_source_set("remote_bitrate_estimator_perf_tests") {
+    testonly = true
+    sources = [
+      "remote_bitrate_estimators_test.cc",
+    ]
+    deps = [
+      ":bwe_simulator_lib",
+    ]
+    if (!build_with_chromium && is_clang) {
+      # Suppress warnings from the Chromium Clang plugin (bugs.webrtc.org/163).
+      suppressed_configs += [ "//build/config/clang:find_bad_constructs" ]
+    }
+  }
 }