Cleanup: Put more plugin code behind the ENABLE_PLUGINS ifdef.

content/public/common/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("//build/config/features.gni")
 import("//content/common/common.gni")
 
 source_set("common") {
   sources = rebase_path(content_common_gypi_values.public_common_sources,
                         ".", "//content")
 
   configs += [
     "//content:content_implementation",
   ]
 
   deps = [
     "//content/common",
     "//skia",
     "//third_party/WebKit/public:blink_headers",
     "//third_party/icu",
   ]
+
+  if (!enable_plugins) {
+    sources -= [
+      "pepper_plugin_info.cc",
+      "pepper_plugin_info.h",
+    ]
+  }
 }