GPU:'Pass' SharedMemory when possible.

This avoids some duplication of shared memory handles just
for the purposes of passing them around. Instead we Map
immediately when the memory arrives in the process, and then
'Pass' the shared memory from there.

BUG=177063, 353822

Review URL: https://codereview.chromium.org/211703003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@259772 0039d316-1c4b-4281-b951-d872f2087c98