This will cause build failed since a include file does not exist.

build/common.gypi

 # Copyright (c) 2011 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.
 
 # IMPORTANT:
 # Please don't directly include this file if you are building via gyp_chromium,
 # since gyp_chromium is automatically forcing its inclusion.
 {
   # Variables expected to be overriden on the GYP command line (-D) or by
   # ~/.gyp/include.gypi.
@@ skipping 109 matching lines @@
       # build (0).
       'inside_chromium_build%': 1,
 
       # Set to 1 to enable fast builds. It disables debug info for fastest
       # compilation.
       'fastbuild%': 0,
 
        # Disable file manager component extension by default.
       'file_manager_extension%': 0,
 
-      # Disable WebUI TaskManager by default.
-      'webui_task_manager%': 0,
-
       # Python version.
       'python_ver%': '2.6',
 
       # Set ARM-v7 compilation flags
       'armv7%': 0,
 
       # Set Neon compilation flags (only meaningful if armv7==1).
       'arm_neon%': 1,
 
       # The system root for cross-compiles. Default: none.
@@ skipping 97 matching lines @@
           'enable_flapper_hacks%': 0,
         }],
 
         # Enable file manager extension by default on Chrome OS.
         ['chromeos==1', {
           'file_manager_extension%': 1,
         }, {
           'file_manager_extension%': 0,
         }],
         
-        # Enable WebUI TaskManager only on Chrome OS and Touch UI.
-        ['chromeos==1 or touchui==1', {
-          'webui_task_manager%': 1,
-        }, {
-          'webui_task_manager%': 0,
-        }],
-
         # Enable smooth scrolling for Linux and ChromeOS
         ['OS=="linux"', {
           'enable_smooth_scrolling%': 1,
         }, {
           'enable_smooth_scrolling%': 0,
         }],
       ],
     },
 
     # Copy conditionally-set variables out one scope.
     'branding%': '<(branding)',
     'buildtype%': '<(buildtype)',
     'target_arch%': '<(target_arch)',
     'host_arch%': '<(host_arch)',
     'library%': 'static_library',
     'toolkit_views%': '<(toolkit_views)',
     'toolkit_uses_pure_views%': '<(toolkit_uses_pure_views)',
     'views_compositor%': '<(views_compositor)',
     'os_posix%': '<(os_posix)',
     'toolkit_uses_gtk%': '<(toolkit_uses_gtk)',
     'use_skia%': '<(use_skia)',
     'use_x11%': '<(use_x11)',
     'use_gnome_keyring%': '<(use_gnome_keyring)',
     'linux_fpic%': '<(linux_fpic)',
     'enable_flapper_hacks%': '<(enable_flapper_hacks)',
     'chromeos%': '<(chromeos)',
     'touchui%': '<(touchui)',
     'webui_certificate_viewer%': '<(webui_certificate_viewer)',
     'file_manager_extension%': '<(file_manager_extension)',
-    'webui_task_manager%': '<(webui_task_manager)',
     'inside_chromium_build%': '<(inside_chromium_build)',
     'fastbuild%': '<(fastbuild)',
     'python_ver%': '<(python_ver)',
     'armv7%': '<(armv7)',
     'arm_neon%': '<(arm_neon)',
     'sysroot%': '<(sysroot)',
     'disable_sse2%': '<(disable_sse2)',
     'component%': '<(component)',
     'use_titlecase_in_grd_files%': '<(use_titlecase_in_grd_files)',
     'use_third_party_translations%': '<(use_third_party_translations)',
@@ skipping 337 matching lines @@
       }],
       ['touchui==1', {
         'grit_defines': ['-D', 'touchui'],
       }],
       ['webui_certificate_viewer==1', {
         'grit_defines': ['-D', 'webui_certificate_viewer'],
       }],
       ['file_manager_extension==1', {
         'grit_defines': ['-D', 'file_manager_extension'],
       }],
-      ['webui_task_manager==1', {
-        'grit_defines': ['-D', 'webui_task_manager'],
-      }],
       ['remoting==1', {
         'grit_defines': ['-D', 'remoting'],
       }],
       ['use_titlecase_in_grd_files==1', {
         'grit_defines': ['-D', 'use_titlecase'],
       }],
       ['use_third_party_translations==1', {
         'grit_defines': ['-D', 'use_third_party_translations'],
         'locales': [
           'ast', 'bs', 'ca@valencia', 'eo', 'eu', 'gl', 'hy', 'ka', 'ku', 'kw',
@@ skipping 85 matching lines @@
       }],
       ['chromeos==1', {
         'defines': ['OS_CHROMEOS=1'],
       }],
       ['touchui==1', {
         'defines': ['TOUCH_UI=1'],
       }],
       ['file_manager_extension==1', {
         'defines': ['FILE_MANAGER_EXTENSION=1'],
       }],
-      ['webui_task_manager==1', {
-        'defines': ['WEBUI_TASK_MANAGER=1'],
-      }],
       ['profiling==1', {
         'defines': ['ENABLE_PROFILING=1'],
       }],
       ['remoting==1', {
         'defines': ['ENABLE_REMOTING=1'],
       }],
       ['p2p_apis==1', {
         'defines': ['ENABLE_P2P_APIS=1'],
       }],
       ['proprietary_codecs==1', {
@@ skipping 1140 matching lines @@
     # settings in target dicts.  SYMROOT is a special case, because many other
     # Xcode variables depend on it, including variables such as
     # PROJECT_DERIVED_FILE_DIR.  When a source group corresponding to something
     # like PROJECT_DERIVED_FILE_DIR is added to a project, in order for the
     # files to appear (when present) in the UI as actual files and not red
     # red "missing file" proxies, the correct path to PROJECT_DERIVED_FILE_DIR,
     # and therefore SYMROOT, needs to be set at the project level.
     'SYMROOT': '<(DEPTH)/xcodebuild',
   },
 }