Revert of [DevTools] Extract platform module.

Source/devtools/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/features.gni")
 
 gypi_values = exec_script(
     "//build/gypi_to_gn.py",
     [ rebase_path("devtools.gypi") ],
     "scope",
     [ "devtools.gypi" ])
 
 # Some of the files in the .gypi use GYP variable expansions, go through and
 # fix them.
 devtools_core_files =
   gypi_values.devtools_core_base_files +
   gypi_values.devtools_bindings_js_files +
   gypi_values.devtools_common_js_files +
   gypi_values.devtools_components_js_files +
   gypi_values.devtools_host_js_files +
   gypi_values.devtools_main_js_files +
-  gypi_values.devtools_platform_js_files +
   gypi_values.devtools_screencast_js_files +
   gypi_values.devtools_sdk_js_files +
   gypi_values.devtools_toolbox_js_files +
   gypi_values.devtools_toolbox_bootstrap_js_files +
   gypi_values.devtools_ui_js_files +
   gypi_values.devtools_workspace_js_files +
   gypi_values.devtools_core_css_files
 
 devtools_extensions_js_files = gypi_values.devtools_extensions_js_files -
   [ "<@(devtools_extension_api_files)" ] +
@@ skipping 276 matching lines @@
   }
 
   concatenate_css("concatenated_devtools_css") {
     app_name = "devtools"
   }
 
   concatenate_css("concatenated_toolbox_css") {
     app_name = "toolbox"
   }
 }