Add a snapshot of flutter/engine/src/build to our sdk

build/android/pylib/efficient_android_directory_copy.sh

Index: build/android/pylib/efficient_android_directory_copy.sh
diff --git a/build/android/pylib/efficient_android_directory_copy.sh b/build/android/pylib/efficient_android_directory_copy.sh
new file mode 100755
index 0000000000000000000000000000000000000000..7021109e273e1b45649159405d14e1f27fe4a7fe
--- /dev/null
+++ b/build/android/pylib/efficient_android_directory_copy.sh
@@ -0,0 +1,78 @@
+#!/system/bin/sh
+
+# Copyright 2014 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+# Android shell script to make the destination directory identical with the
+# source directory, without doing unnecessary copies. This assumes that the
+# the destination directory was originally a copy of the source directory, and
+# has since been modified.
+
+source=$1
+dest=$2
+echo copying $source to $dest
+
+delete_extra() {
+  # Don't delete symbolic links, since doing so deletes the vital lib link.
+  if [ ! -L "$1" ]
+  then
+    if [ ! -e "$source/$1" ]
+    then
+      echo rm -rf "$dest/$1"
+      rm -rf "$dest/$1"
+    elif [ -d "$1" ]
+    then
+      for f in "$1"/*
+      do
+       delete_extra "$f"
+      done
+    fi
+  fi
+}
+
+copy_if_older() {
+  if [ -d "$1" ] && [ -e "$dest/$1" ]
+  then
+    if [ ! -e "$dest/$1" ]
+    then
+      echo cp -a "$1" "$dest/$1"
+      cp -a "$1" "$dest/$1"
+    else
+      for f in "$1"/*
+      do
+        copy_if_older "$f"
+      done
+    fi
+  elif [ ! -e "$dest/$1" ] || [ "$1" -ot "$dest/$1" ] || [ "$1" -nt "$dest/$1" ]
+  then
+    # dates are different, so either the destination of the source has changed.
+    echo cp -a "$1" "$dest/$1"
+    cp -a "$1" "$dest/$1"
+  fi
+}
+
+if [ -e "$dest" ]
+then
+  echo cd "$dest"
+  cd "$dest"
+  for f in ./*
+  do
+    if [ -e "$f" ]
+    then
+      delete_extra "$f"
+    fi
+  done
+else
+  echo mkdir "$dest"
+  mkdir "$dest"
+fi
+echo cd "$source"
+cd "$source"
+for f in ./*
+do
+  if [ -e "$f" ]
+  then
+    copy_if_older "$f"
+  fi
+done