Fixes compile and gn-check errors with enable_plugins=false.

content/public/child/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.
 
+import("//ppapi/features/features.gni")
+
 # See //content/BUILD.gn for how this works.
 group("child") {
   if (is_component_build) {
     public_deps = [
       "//content",
     ]
   } else {
     public_deps = [
       ":child_sources",
     ]
     if (!is_android) {
-      public_deps += [
-        "//content/gpu",
-        "//content/ppapi_plugin",
-      ]
+      public_deps += [ "//content/gpu" ]
+    }
+    if (enable_plugins) {
+      public_deps += [ "//content/ppapi_plugin" ]
     }
   }
 }
 
 source_set("child_sources") {
   # External code should depend in via ":child" above.
   visibility = [ "//content/*" ]
 
   sources = [
     "child_thread.h",
@@ skipping 16 matching lines @@
     "//content/public/common:common_sources",
     "//gin",
   ]
 
   allow_circular_includes_from = [
     # This target is a pair with content/child. They always go together and
     # include headers from each other.
     "//content/child",
   ]
 }