Put Data Reduction Proxy support in Cronet behind a gyp flag

components/cronet/cronet_static.gypi

 # 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.
 
 {
   # This target is included into both 'cronet_static' and 'cronet_static_small'.
   'type': 'static_library',
   'dependencies': [
     '../base/base.gyp:base',
     '../base/third_party/dynamic_annotations/dynamic_annotations.gyp:dynamic_annotations',
     'cronet_jni_headers',
     'cronet_url_request_context_config_list',
     'cronet_url_request_java',
     'cronet_version',
     'metrics',
   ],
   'sources': [
     'android/chromium_url_request.cc',
     'android/chromium_url_request.h',
     'android/chromium_url_request_context.cc',
     'android/chromium_url_request_context.h',
     'android/chromium_url_request_error_list.h',
     'android/chromium_url_request_priority_list.h',
-    'android/cronet_data_reduction_proxy.cc',
-    'android/cronet_data_reduction_proxy.h',
     'android/cronet_histogram_manager.cc',
     'android/cronet_histogram_manager.h',
     'android/cronet_library_loader.cc',
     'android/cronet_library_loader.h',
     'android/cronet_in_memory_pref_store.cc',
     'android/cronet_in_memory_pref_store.h',
     'android/cronet_upload_data_stream_adapter.cc',
     'android/cronet_upload_data_stream_adapter.h',
     'android/cronet_upload_data_stream_delegate.cc',
     'android/cronet_upload_data_stream_delegate.h',
@@ skipping 23 matching lines @@
     '-Wno-sign-promo',
     '-Wno-missing-field-initializers',
   ],
   'ldflags': [
     '-llog',
     '-landroid',
     '-Wl,--gc-sections',
     '-Wl,--exclude-libs,ALL'
   ],
 }