introduce helper script diff-upstream.sh

scripts/config.sh

@@ -30,5 +30,6 @@ CSS_PROPERTIES_COPY="$DEVTOOLS_ROOT/CSSProperties.in"
 CSS_PROPERTIES_OUTPUT_FILE="$DEVTOOLS_ROOT/front_end/SupportedCSSProperties.js"
 INSPECTOR_BACKEND_COMMANDS_OUTPUT_FILE="$DEVTOOLS_ROOT/front_end/InspectorBackendCommands.js"
 SCRIPTS="$ROOT/scripts"
+DIFF_WORK_DIR="$ROOT/../diff-upstream"
 
 popd .

scripts/diff-upstream.sh

@@ -0,0 +1,29 @@
+#!/usr/bin/env bash
+
+set -e
+
+. "$(dirname "${BASH_SOURCE[0]}")/config.sh"
+
+pushd "$ROOT"
+
+MESSAGE=$(git log -1 HEAD --pretty=format:%s)
+
+if [[ ! "$MESSAGE" == *"merge updates from official devtools"* ]]; then
+  echo "run ./scripts/squash-and-merge-official-updates.sh before diffing"
+  echo "unmerged changes would appear in the diff"
+  exit 1
+fi
+
+if [ -d "$DIFF_WORK_DIR" ] ; then
+  rm -rf "$DIFF_WORK_DIR"
+fi
+
+git clone "$ROOT" "$DIFF_WORK_DIR" --branch "$DEVTOOLS_BRANCH"
+
+pushd "$DIFF_WORK_DIR"
+
+cp -r "$DEVTOOLS_ROOT"/* .
+
+gitup
+
+popd