Revert 168921 - Beginnings of moving more stuff from build_sdk.py to GYP.

Revert 168921 - Beginnings of moving more stuff from build_sdk.py to GYP.

Adds a new target to all.gyp: chromium_builder_nacl_sdk
Adds a native_client_sdk gyp file: it depends on nacl_core_sdk from the
native_client repo, but also builds and copies ppapi libraries to the toolchain
directories.

Retry of http://codereview.chromium.org/11299081/.
Which was a retry of http://codereview.chromium.org/11363045/.

Failed both times because of a separate NaCl build issue that was resolved by
http://crrev.com/168621.

BUG=none
TBR=noelallen@chromium.org

Review URL: https://codereview.chromium.org/11413075

TBR=binji@chromium.org
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=168934