Fix the Chrome Mac build.
Fix the Chrome Mac build.

Previously, we were including two different copies of the PPAPI CPP library.
In Xcode, this objects got the same ID but were different, which caused GYP to
throw an error.

In this patch, we exclude the non-Chrome version of the PPAPI plugin in the
Chrome version of plugin.xcodeproj.

Review URL: http://codereview.chromium.org/6073007

git-svn-id: 721b910a23eff8a86f00c8fd261a7587cddf18f8@4064 fcba33aa-ac0c-11dd-b9e7-8d5594d729c2

sbc100/native_client,nacl-webkit/native_client,sbc100/native_client,nacl-webkit/native_client,sbc100/native_client,nacl-webkit/native_client,sbc100/native_client,sbc100/native_client,nacl-webkit/native_client,sbc100/native_client,nacl-webkit/native_client