Remove HTML swapped out image export tests

It crashes on master for some reason. Since it's not
in our main focus it's simpler to remove it.

Change-Id: I2d595bf18abc4f22fac2c16b37247a23fd271c3d
Optimize ImplCheckSizeOfSwappedInGraphics() a bit

Store used size as a member so we don't need to recalculate it
all the time and no need to use a size map.

Change-Id: I1f929c5d3a56f545cef123bda087ecaf8ca0be4a
Update notes about swapping

Change-Id: I6b9f5f9c4a0bc87376a469835a50dc2cf598479e