pdf: Create a separate component for using the pdf pepper plugin.

components/pdf/browser/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.
 
-source_set("browser") {
+import("//build/config/features.gni")
+
+static_library("browser") {
   sources = [
-    "cdm_message_filter_android.cc",
-    "cdm_message_filter_android.h",
+    "open_pdf_in_reader_prompt_delegate.h",
+    "pdf_tab_helper.cc",
+    "pdf_tab_helper.h",
+    "pdf_tab_helper_delegate.h",
   ]
 
   deps = [
-    "//base",
-    "//components/cdm/common",
+    "//components/pdf/common",
     "//content/public/browser",
-    "//content/public/common",
-    "//media",
   ]
 }