Add ijar to third_party and use it for generating .jar.toc files in GN

third_party/ijar/BUILD.gn

+# Copyright 2015 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.
+
+# A tool that removes all non-interface-specific parts from a .jar file.
+
+if (current_toolchain == host_toolchain) {
+  executable("ijar") {
+    sources = [
+      "classfile.cc",
+      "common.h",
+      "ijar.cc",
+      "zip.cc",
+      "zip.h",
+    ]
+
+    # Always build release since this is a build tool.
+    if (is_debug) {
+      configs -= [ "//build/config:debug" ]
+      configs += [ "//build/config:release" ]
+    }
+    ldflags = [ "-lz" ]
+    deps = [
+      "//build/config/sanitizers:deps",
+    ]
+  }
+}