In Chrome - when editing a block when there is a nearby embedded media video
block can cause the video part of the block to display over the config
form making it hard to do editing.

From what the interweb says this is a problem with wmode needing to be
set.

Change-Id: I8cd2a9c20ac2e14fe52274aeafeead96a7e94c17
Signed-off-by: Robert Lyon <robertl@catalyst.net.nz>