plugins: eliminate use of product_dir
plugins: eliminate use of product_dir

The 'product_dir' variable in gyp is only implemented by the
scons generator and only used by plugins, and the
plugin tests don't yet run on Linux (where we use scons).

The npapi_layout_test_plugin is copied into the proper place
for layout tests with a 'copy' rule.

BUG=15695

Review URL: http://codereview.chromium.org/150085

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@19645 0039d316-1c4b-4281-b951-d872f2087c98

Crystalnix/house-of-life-chromium,gavinp/chromium,gavinp/chromium,Crystalnix/house-of-life-chromium,ropik/chromium,Crystalnix/house-of-life-chromium,yitian134/chromium,Crystalnix/house-of-life-chromium,yitian134/chromium,yitian134/chromium,gavinp/chromium,ropik/chromium,adobe/chromium,Crystalnix/house-of-life-chromium,gavinp/chromium,gavinp/chromium,yitian134/chromium,adobe/chromium,yitian134/chromium,adobe/chromium,Crystalnix/house-of-life-chromium,ropik/chromium,ropik/chromium,gavinp/chromium,Crystalnix/house-of-life-chromium,yitian134/chromium,adobe/chromium,ropik/chromium,gavinp/chromium,yitian134/chromium,adobe/chromium,yitian134/chromium,Crystalnix/house-of-life-chromium,ropik/chromium,gavinp/chromium,Crystalnix/house-of-life-chromium,adobe/chromium,yitian134/chromium,adobe/chromium,ropik/chromium,ropik/chromium,Crystalnix/house-of-life-chromium,yitian134/chromium,adobe/chromium,gavinp/chromium,ropik/chromium,adobe/chromium,Crystalnix/house-of-life-chromium,gavinp/chromium,adobe/chromium,adobe/chromium