Update the names of some parameters passed to contextMenu onclick handlers....

Update the names of some parameters passed to contextMenu onclick handlers.

This changes the mediaType parameter values to be lowercase (eg "audio" instead
of "AUDIO"), and changes mainFrameUrl to be pageUrl as the design doc had 
intended.

BUG=49725
TEST=In onclick handlers, values for mediaType should be lowercase and there
should be a pageUrl property matching the url of the page.


Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=54999

[Aaron Boodman, 2010-08-04 22:24:42]

lgtm