Add .wprgo to tools/perf/page_sets/.gitignore

Bug: 730036
Change-Id: Id7e081e62853b7497e7c6e6c43aac3063bf4dd67
Reviewed-on: https://chromium-review.googlesource.com/574456Reviewed-by: Helen Li <xunjieli@chromium.org>
Commit-Queue: Ned Nguyen <nednguyen@google.com>
Cr-Commit-Position: refs/heads/master@{#487108}

tools/perf/page_sets/.gitignore

@@ -10,3 +10,4 @@
 *.wav
 *.webm
 *.wpr
+*.wprgo