Add GDB auto-load file to the output directory.

chrome/BUILD.gn

Index: chrome/BUILD.gn
diff --git a/chrome/BUILD.gn b/chrome/BUILD.gn
index ec0d8ddd0df924fc62690bb0e9c142af429c3a8f..b8a6ebcf225d2b81042ac12d26ad1b3eb774eefe 100644
--- a/chrome/BUILD.gn
+++ b/chrome/BUILD.gn
@@ -275,6 +275,8 @@ if (!is_android && !is_mac) {
       defines += [ "CHROME_MULTIPLE_DLL" ]
       data_deps += [ ":chrome_child" ]
     }
+
+    data_deps += [ ":gdb_auto_load" ]
   }
 }  # !is_android && !is_mac
 
@@ -1618,3 +1620,16 @@ if (is_linux) {
     ]
   }
 }
+
+# When this auto-load file is installed in the same directory as the Chromium
+# executable, it automatically registers pretty-printers when you start GDB [1].
+#
+# [1] https://sourceware.org/gdb/current/onlinedocs/gdb/Writing-a-Pretty_002dPrinter.html
+copy("gdb_auto_load") {
+  sources = [
+    "//tools/gdb/chrome-gdb.py",
+  ]
+  outputs = [
+    "$root_out_dir/chrome-gdb.py",
+  ]
+}