Flip 'Linux x64' bot on chromium waterfall to GN.

BUILD.gn

Index: BUILD.gn
diff --git a/BUILD.gn b/BUILD.gn
index edce1e20776a44ad9d9b0a578fe5479317d22bb4..71e625690a5a6f3cf3c80585867d717334d58e03 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -809,7 +809,12 @@ group("chromium_builder_perf") {
       deps += [ "//chrome/test:performance_browser_tests" ]
     }
     if (is_linux && !is_chromeos) {
-      deps += [ "//chrome:linux_symbols" ]
+      if (is_official_build) {
+        # In GN builds, this is controlled by the 'linux_dump_symbols'
+        # flag, which defaults to 1 for official builds. For now,
+        # we skip the separate flag and just key off of is_official_build.
+        deps += [ "//chrome:linux_symbols" ]
+      }
 
       if (!is_chromeos) {
         deps += [ "//tools/perf/clear_system_cache" ]