Remove all the browser side extensions code from Android.

chrome/browser/extensions/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/crypto.gni")
 import("//build/config/features.gni")
 import("//build/config/ui.gni")
 
 gypi_values = exec_script(
     "//build/gypi_to_gn.py",
     [ rebase_path("../../chrome_browser_extensions.gypi") ],
     "scope",
     [ "../../chrome_browser_extensions.gypi" ])
 
 # GYP version: chrome/chrome_browser_extensions.gypi:browser_extensions
 static_library("extensions") {
-  sources = rebase_path(
-      gypi_values.chrome_browser_extensions_extensions_sources,
-      ".", "//chrome")
-
+  sources = []
   defines = []
 
   # TODO(GYP) remove this when webrtc is ported.
   configs += [ "//content:webrtc_stub_config" ]
 
   # Since browser and browser_extensions actually depend on each other,
   # we must omit the dependency from browser_extensions to browser.
   # However, this means browser_extensions and browser should more or less
   # have the same dependencies. Once browser_extensions is untangled from
   # browser, then we can clean up these dependencies.
@@ skipping 188 matching lines @@
           ".", "//chrome")
     }
 
     if (!use_ozone) {
       sources -= [
         "global_shortcut_listener_ozone.cc",
       ]
     }
   }
 }