Add wrapper for compare script to run gyp and gn

tools/gn/bin/compare_flags.sh

Index: tools/gn/bin/compare_flags.sh
diff --git a/tools/gn/bin/compare_flags.sh b/tools/gn/bin/compare_flags.sh
new file mode 100755
index 0000000000000000000000000000000000000000..ed8f5dce126ee6f568b16eb99ccee0245bc04bbf
--- /dev/null
+++ b/tools/gn/bin/compare_flags.sh
@@ -0,0 +1,16 @@
+#!/bin/bash
+
+# Compare gyp compile flags to GN compile flags. Currently only Release
+# non-component.
+if [ $# -ne 1 ]
+then
+  echo "Usage: $0 target_name"
+  exit 65
+fi
+GYP_DEFINES=
+python build/gyp_chromium -Goutput_dir=out_gyp_flags -Gconfig=Release && \
+gn gen out/gn_flags --args="is_debug=false is_component_build=false" && \
+ninja -C out_gyp_flags/Release -t commands $1 > gyp_flags_$1.txt && \
+ninja -C out/gn_flags -t commands $1 > gn_flags_$1.txt && \
+python tools/gn/bin/gyp_flag_compare.py gyp_flags_$1.txt gn_flags_$1.txt > compare_flags_$1.txt ; \
+echo "Wrote compare_flags_$1.txt"