Add WebPluginContainerTests for plugins without copy permissions

Allows creating TestPlugin without copy permissions, so that we can
make sure that copy operations from using command, Ctrl+C and context
menu will add an empty string to the clipboard.

Bug: 1380985
Change-Id: I0f5bd60155969aa8fd8ddd285c94d4c7994d94f0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4060582


Reviewed-by: Dave Tapuska <dtapuska@chromium.org>
Commit-Queue: Nigi <nigi@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1076499}