The main motive for this patch is to remove the use of the GlobalManager
global (which was used to see if an extension ID is valid, which was
specifically added in order to create thebrowser_ext_lastError.js test).
To preserve test coverage I implemented a full validation of the
runtime.sendMessage method.
Now the error for a non-existent extension is identical in both the
content script and background pages. Note that this also fixes a
minor privacy leak: Previously extensions could see whether another
extension is installed by sending a message to the specified extension
and using the different responses to see whether another extension is
installed.
MozReview-Commit-ID: 82R97Ei25Xr
47e975c1fb
