add script for rolling flutter_embedder.h

Author: ardera

tools/roll_embedder_header.sh

@@ -0,0 +1,11 @@
+#!/bin/sh
+
+ENGINE_VERSION="$(curl -s https://raw.githubusercontent.com/flutter/flutter/stable/bin/internal/engine.version)"
+
+if [ ! -f "third_party/flutter_embedder_header/include/flutter_embedder.h" ]; then
+    echo "Incorrect working directory. Please launch this script with the flutter-pi repo root as the working directory, using 'tools/roll_embedder_header.sh'.".
+    exit 1
+fi
+
+curl -o third_party/flutter_embedder_header/include/flutter_embedder.h "https://raw.githubusercontent.com/flutter/engine/$ENGINE_VERSION/shell/platform/embedder/embedder.h"
+echo "$ENGINE_VERSION" > third_party/flutter_embedder_header/engine.version