Mark some files/targets as compiled only when their associated feature is enabled.

chrome/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.
 
 import("//build/config/crypto.gni")
 import("//build/config/features.gni")
 import("//build/config/ui.gni")
 import("//components/nacl/nacl_defines.gni")
 import("//tools/grit/grit_rule.gni")
 
@@ skipping 120 matching lines @@
     #        '<(SHARED_INTERMEDIATE_DIR)/chrome/browser/metrics/variations/generated_resources_map.cc',
 
     defines = nacl_defines
 
     # TODO(GYP) remove this when the real webrtc target is used below.
     configs += [ "//content:webrtc_stub_config" ]
 
     deps += [
       "//cc",
       "//chrome/browser/performance_monitor",
-      "//chrome/browser/sync_file_system:sync_file_system_proto",
-      "//chrome/browser/sync_file_system/drive_backend:sync_file_system_drive_proto",
       "//chrome/common/extensions/api:api",
       "//components/autofill/content/browser",
       "//components/dom_distiller/content",
       "//components/keyed_service/content",
       "//components/storage_monitor",
       "//components/translate/content/browser",
       "//components/url_matcher",
       "//components/usb_service",
       "//components/visitedlink/browser",
       "//components/visitedlink/common",
@@ skipping 72 matching lines @@
       #"app_shim"  TODO(GYP)
     ]
   }
   if (cld2_data_source == "component") {
     sources += [
       "component_updater/cld_component_installer.cc",
       "component_updater/cld_component_installer.h",
     ]
   }
   if (enable_extensions) {
-    deps += [ "//chrome/browser/extensions" ]
+    deps += [
+      "//chrome/browser/extensions",
+      "//chrome/browser/sync_file_system:sync_file_system_proto",
+      "//chrome/browser/sync_file_system/drive_backend:sync_file_system_drive_proto",
+    ]
     sources += rebase_path(gypi_values.chrome_browser_extensions_sources,
                            ".", "//chrome")
   }
   if (enable_background) {
     sources += rebase_path(gypi_values.chrome_browser_background_sources,
                            ".", "//chrome")
     if (!use_aura || is_win) {
       sources -= [ "background/background_mode_manager_aura.cc" ]
     }
   }
@@ skipping 412 matching lines @@
 # TODO(GYP) write internal action
 if (false) {  #if (is_chrome_branded) {
   action("chrome_internal_resources_gen") {
     # TODO(GYP)
   }
 } else {
   group("chrome_internal_resources_gen") {
     # Empty placeholder.
   }
 }