Fix gn builds never being clean at symbol_level = 0

chrome/BUILD.gn

Index: chrome/BUILD.gn
diff --git a/chrome/BUILD.gn b/chrome/BUILD.gn
index 7024bd3852e70da2839796a73b488c6c6ea6a64f..1de5ec6b0de6b5e33494aa23c37b0e22c86400f3 100644
--- a/chrome/BUILD.gn
+++ b/chrome/BUILD.gn
@@ -52,8 +52,10 @@ if (is_win) {
     ]
     outputs = [
       "$root_out_dir/chrome.exe",
-      "$root_out_dir/chrome.exe.pdb",
     ]
+    if (symbol_level != 0) {
+      outputs += [ "$root_out_dir/chrome.exe.pdb" ]
+    }
     args = [
       "-i",
       rebase_path("$root_out_dir/initialexe", root_build_dir),