Fix nan definition on GN Android build.

This resulted in a double -D definition.

TBR=scottmg

Review URL: https://codereview.chromium.org/132903005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@244203 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 244203