Add devtools resources rules to the GN build.

public/BUILD.gn

 # 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.
 
 config("blink_headers_config") {
   include_dirs = [ ".." ]
 }
 
 # Depend on this target to use public blink API headers for things like enums
 # and public structures without actually linking against any Blink libraries.
 source_set("blink_headers") {
   direct_dependent_configs = [ ":blink_headers_config" ]
 }
+
+group("blink_devtools_frontend_resources") {
+  deps = [
+    "//third_party/WebKit/Source/devtools:devtools_frontend_resources",
+  ]
+}
+
+group("blink_generate_devtools_grd") {
+  deps = [
+    "//third_party/WebKit/Source/devtools:generate_devtools_grd",
+  ]
+}