Cleanup: Put more plugin code behind the ENABLE_PLUGINS ifdef.

content/public/common/BUILD.gn

Index: content/public/common/BUILD.gn
diff --git a/content/public/common/BUILD.gn b/content/public/common/BUILD.gn
index 0906507b8bbee522de3613476ef042ae2d6fa4b1..8e1038dccbcfb367678ae2ee81c57e4ec3a9f517 100644
--- a/content/public/common/BUILD.gn
+++ b/content/public/common/BUILD.gn
@@ -2,6 +2,7 @@
 # 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") {
@@ -18,4 +19,11 @@ source_set("common") {
     "//third_party/WebKit/public:blink_headers",
     "//third_party/icu",
   ]
+
+  if (!enable_plugins) {
+    sources -= [
+      "pepper_plugin_info.cc",
+      "pepper_plugin_info.h",
+    ]
+  }
 }