Bug 1055865 patch 1 - Add reftest for sizing of empty ::first-letter.  r=jfkthame

This test fails without the patch series because the border around the
test is too tall, but patch 5 reduces the height of the border in the
test so that it matches the reference.
Bug 1055865 patch 2 - Use separate nsHTMLReflowMetrics for reflowing the child of the nsFirstLetterFrame.  r=jfkthame

This changes this code to do things in the normal way, which is to use a
separate nsHTMLReflowMetrics for each Reflow, rather than (as this code
was) reusing the one for the nsFirstLetterFrame for its text frame
child.
Bug 1055865 patch 3 - Fork a bit of code between the floating and non-floating branches in nsFirstLetterFrame::Reflow.  r=jfkthame

This patch makes no changes other than duplicating the code previously
after the if/else on both branches of the if/else.

The next two patches in this series will completely rewrite the half in
the non-floating (i.e., inline) codepath (the else branch).
Bug 1055865 patch 4 - Remove bits of code that nsLineLayout takes care of.  r=jfkthame

There's no need for these calls to be done in the inline ::first-letter
codepath.

In particular, nsLineLayout::ReflowFrame (called a few lines above)
calls SetRect and DidReflow, while nsLineLayout::RelativePositionFrames
(which is called at the end of inline reflow) calls
FinishAndStoreOverflow.
Bug 1055865 patch 5 - Use normal inline handling for setting the size of a non-floating nsFirstLetterFrame.  r=jfkthame

This is the actual fix for the bug.  This changes the vertical sizing of
inline ::first-letter frames to work like inlines (and size based on
font metrics), so that the line-height calculation that happens later
will produces the same results as inlines would produce.

In the case we're concerned with of having a text frame child that's
0x0, this changes the inline ::first-letter from from being 0x0 to
having a height that is determined from the font metrics.
Bug 839812 - Add clip-path style for fullscreen override, which was probably originally intended ("SVG masking, clipping, or filtering").  r=dholbert