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

build/secondary/tools/grit/repack.gni

Index: build/secondary/tools/grit/repack.gni
diff --git a/build/secondary/tools/grit/repack.gni b/build/secondary/tools/grit/repack.gni
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+# 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.
+
+# This file defines a template to invoke grit repack in a consistent manner.
+#
+# Parameters:
+#   sources  [required]
+#       List of pak files that need to be combined.
+#
+#   output  [required]
+#       File name (single string) of the output file.
+#
+#   repack_options  [optional]
+#       List of extra arguments to pass.
+#
+#   deps  [optional]
+#   visibility  [optional]
+#       Normal meaning.
+template("repack") {
+  action(target_name) {
+    assert(defined(invoker.sources), "Need sources for $target_name")
+    assert(defined(invoker.output), "Need output for $target_name")
+
+    if (defined(invoker.visibility)) {
+      visibility = invoker.visibility
+    }
+
+    script = "//tools/grit/grit/format/repack.py"
+
+    inputs = invoker.sources
+    outputs = [
+      invoker.output,
+    ]
+
+    args = []
+    if (defined(invoker.repack_options)) {
+      args += invoker.repack_options
+    }
+    args += [ rebase_path(invoker.output, root_build_dir) ]
+    args += rebase_path(invoker.sources, root_build_dir)
+
+    if (defined(invoker.deps)) {
+      deps = invoker.deps
+    }
+  }
+}