Fix clipboardData API path on copy

Newer versions of Chrome return undefined for DataTransfer#setData
however we can still check for the presence of a fully featured
DataTransfer object by checking for the 'items' property.

Unfortunately this isn't robust feature detection so we'll need to
monitor the situation.

Change-Id: I52fbbe7597f4779b07c619a1ce601b9a7f504cc4