Speed up interop patch file creation

tools/dartium/generate_patches.sh

+#!/usr/bin/env bash
+#
+
+set -x
+
+#   generate_patches.sh [systems]
+#
+# Convenience script to generate patches for JsInterop under Dartium.  Do not call from build steps or tests
+# - call fremontcutbuilder and dartdomgenerator instead. Do not add 'real'
+# functionality here - change the python code instead.
+#
+# I find it essential to generate all the systems so I know if I am breaking
+# other systems.  My habit is to run:
+#
+#   ./go.sh
+
+# 1. After running go.sh libraries in sdk/lib may change.
+# 2. Build Dartium.
+# 3. Run this script and sdk/lib/js/dartium/cached_patches will be created.
+# 4. Rebuild Dartium.
+# 5. Commit files in sdk/lib
+
+LOCATION_DARTIUM="../../../out/Release"
+DARTIUM="$LOCATION_DARTIUM"
+
+DART_APP_LOCATION="file://"$PWD"/generate_app/generate_cached_patches.html"
+DARTIUM_ARGS=" --user-data-dir=out --disable-web-security --no-sandbox --enable-logging=stderr"
+CACHED_PATCHES_FILE=""$PWD"/../../sdk/lib/js/dartium/cached_patches.dart"
+
+if [[ "$1" != "" ]] ; then
+  DARTIM="$1"
+fi
+
+cmd=""$DARTIUM"/chrome "$DARTIUM_ARGS" "$DART_APP_LOCATION" 3>&1 1>&2- 2>&3 | \
+  (sed -n '/START_OF_CACHED_PATCHES/,/END_OF_CACHED_PATCHES/p') > "$CACHED_PATCHES_FILE""
+
+reset && eval "${cmd}"
+
+