Revert of [NaCl SDK] Remove create_nmf dependency on NACL_SDK_ROOT env var

Revert of [NaCl SDK] Remove create_nmf dependency on NACL_SDK_ROOT env var (patchset #5 id:80001 of https://codereview.chromium.org/737653003/)

Reason for revert:
Broke compile on Google Chrome ChromeOS bot.

[8069/19495] CXX obj/components/policy/core/common/cloud/policy_component_common.external_policy_data_updater.o
FAILED: cd ../../third_party/liblouis; python ../../native_client_sdk/src/tools/create_nmf.py ../../out/Release/chromevox_test_data/braille/liblouis_nacl_x86_64.nexe "--output=../../out/Release/chromevox_test_data/braille/liblouis_nacl.nmf"
Traceback (most recent call last):
  File "../../native_client_sdk/src/tools/create_nmf.py", line 680, in <module>
    rtn = main(sys.argv[1:])
  File "../../native_client_sdk/src/tools/create_nmf.py", line 633, in main
    options.lib_path += GetDefaultLibPath(config)
  File "../../native_client_sdk/src/tools/create_nmf.py", line 507, in GetDefaultLibPath
    sdk_root = GetSDKRoot()
  File "../../native_client_sdk/src/tools/create_nmf.py", line 478, in GetSDKRoot
    assert(os.path.exists(os.path.join(sdk_root, 'toolchain')))
AssertionError
ninja: build stopped: subcommand failed.

http://build.chromium.org/p/chromium.chrome/builders/Google%20Chrome%20ChromeOS/builds/76569

Original issue's description:
> [NaCl SDK] Remove create_nmf dependency on NACL_SDK_ROOT env var
>
> create_nmf should determine the root of the SDK relative
> to its own location.
>
> The exception to this is when its run as part of the
> chrome build, when it is not yet installed.  In this
> case we pass --no-default-libpath and --objdump to
> create_nmf to remove any use of the SDK root.
>
> Committed: https://crrev.com/088561ac99314a79866a39f79bb32bd5e1196217
> Cr-Commit-Position: refs/heads/master@{#313957}

TBR=binji@chromium.org,dmichael@chromium.org,sbc@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true

Committed: https://crrev.com/243315bb066856bcadc20b3118ec623d96187edd
Cr-Commit-Position: refs/heads/master@{#313963}

[please use gerrit instead, 2015-01-30 19:34:33]

Created Revert of [NaCl SDK] Remove create_nmf dependency on NACL_SDK_ROOT env
var

[commit-bot: I haz the power, 2015-01-30 19:35:37]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/890033003/1

[commit-bot: I haz the power, 2015-01-30 19:37:14]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-01-30 19:37:59]

Patchset 1 (id:??) landed as
https://crrev.com/243315bb066856bcadc20b3118ec623d96187edd
Cr-Commit-Position: refs/heads/master@{#313963}

[Sam Clegg, 2015-01-30 20:24:09]

lgtm.  Why did the trybots find this?

[please use gerrit instead, 2015-01-30 20:28:42]

Not sure.