Sorry, this is not building for me and I don't know why ATM.  This is both in precise and oneiric chroots.
cd /«PKGBUILDDIR»/build-tree/src && GYP_GENERATORS=make GYP_DEFINES="disable_sse2=1 use_third_party_translations=1 werror= target_arch=x64 werror= linux_sandbox_path=/usr/lib/chromium-browser/chromium-browser-sandbox linux_sandbox_chrome_path=/usr/lib/chromium-browser/chromium-browser  proprietary_codecs=1 build_ffmpegsumo=0 " python build/gyp_chromium --no-circular-check build/all.gyp
Updating projects from gyp files...
Traceback (most recent call last):
  File "build/gyp_chromium", line 171, in <module>
    sys.exit(gyp.main(args))
  File "/«PKGBUILDDIR»/build-tree/src/tools/gyp/pylib/gyp/__init__.py", line 465, in main
    options.circular_check)
  File "/«PKGBUILDDIR»/build-tree/src/tools/gyp/pylib/gyp/__init__.py", line 101, in Load
    depth, generator_input_info, check, circular_check)
  File "/«PKGBUILDDIR»/build-tree/src/tools/gyp/pylib/gyp/input.py", line 2265, in Load
    depth, check)
  File "/«PKGBUILDDIR»/build-tree/src/tools/gyp/pylib/gyp/input.py", line 435, in LoadTargetBuildFile
    includes, depth, check)
  File "/«PKGBUILDDIR»/build-tree/src/tools/gyp/pylib/gyp/input.py", line 435, in LoadTargetBuildFile
    includes, depth, check)
  File "/«PKGBUILDDIR»/build-tree/src/tools/gyp/pylib/gyp/input.py", line 389, in LoadTargetBuildFile
    build_file_path)
  File "/«PKGBUILDDIR»/build-tree/src/tools/gyp/pylib/gyp/input.py", line 986, in ProcessVariablesAndConditionsInDict
    ProcessConditionsInDict(the_dict, is_late, variables, build_file)
  File "/«PKGBUILDDIR»/build-tree/src/tools/gyp/pylib/gyp/input.py", line 863, in ProcessConditionsInDict
    variables, build_file)
  File "/«PKGBUILDDIR»/build-tree/src/tools/gyp/pylib/gyp/input.py", line 1012, in ProcessVariablesAndConditionsInDict
    build_file)
  File "/«PKGBUILDDIR»/build-tree/src/tools/gyp/pylib/gyp/input.py", line 1027, in ProcessVariablesAndConditionsInList
    ProcessVariablesAndConditionsInDict(item, is_late, variables, build_file)
  File "/«PKGBUILDDIR»/build-tree/src/tools/gyp/pylib/gyp/input.py", line 986, in ProcessVariablesAndConditionsInDict
    ProcessConditionsInDict(the_dict, is_late, variables, build_file)
  File "/«PKGBUILDDIR»/build-tree/src/tools/gyp/pylib/gyp/input.py", line 863, in ProcessConditionsInDict
    variables, build_file)
  File "/«PKGBUILDDIR»/build-tree/src/tools/gyp/pylib/gyp/input.py", line 1012, in ProcessVariablesAndConditionsInDict
    build_file)
  File "/«PKGBUILDDIR»/build-tree/src/tools/gyp/pylib/gyp/input.py", line 1027, in ProcessVariablesAndConditionsInList
    ProcessVariablesAndConditionsInDict(item, is_late, variables, build_file)
  File "/«PKGBUILDDIR»/build-tree/src/tools/gyp/pylib/gyp/input.py", line 1012, in ProcessVariablesAndConditionsInDict
    build_file)
  File "/«PKGBUILDDIR»/build-tree/src/tools/gyp/pylib/gyp/input.py", line 1031, in ProcessVariablesAndConditionsInList
    expanded = ExpandVariables(item, is_late, variables, build_file)
  File "/«PKGBUILDDIR»/build-tree/src/tools/gyp/pylib/gyp/input.py", line 698, in ExpandVariables
    (contents, p.returncode))
Exception: Call to 'python build_nacl_irt.py --inputs --platform=x86-64' returned exit status 2. while loading dependencies of chrome/browser/sync/tools/sync_tools.gyp while loading dependencies of build/all.gyp while trying to load build/all.gyp