Don't fail at gyp time if arm-sysroot is missing.

build/common.gypi

 # Copyright (c) 2012 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 579 matching lines @@
         }, {
           'enable_settings_app%': 0,
         }],
 
         ['OS=="linux" and target_arch=="arm" and chromeos==0', {
           # Set some defaults for arm/linux chrome builds
           'armv7%': 1,
           'linux_breakpad%': 0,
           'linux_use_tcmalloc%': 0,
           'linux_use_gold_flags%': 0,
-          # sysroot need to be an absolute path otherwise it generates
+          # sysroot needs to be an absolute path otherwise it generates
           # incorrect results when passed to pkg-config
-          'sysroot%': '<!(cd <(DEPTH)/arm-sysroot && pwd -P)',
+          'sysroot%': '<!(cd <(DEPTH) && pwd -P)/arm-sysroot',
         }], # OS=="linux" and target_arch=="arm" and chromeos==0
       ],
 
       # Set this to 1 to use the Google-internal file containing
       # official API keys for Google Chrome even in a developer build.
       # Setting this variable explicitly to 1 will cause your build to
       # fail if the internal file is missing.
       #
       # Set this to 0 to not use the internal file, even when it
       # exists in your checkout.
@@ skipping 3316 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',
   },
 }