Allow resolution to be configured on command line. Default to 1280x1024.
Change default back to 800x600 as mac travis builders don't work with 1280x1024
Change opts to work in screen pixels that are scaled to device pixels.
Merge pull request #3398 from glennw/config-res

Allow resolution to be configured on command line. Default to 1280x1024.

Reviewed-by: SimonSapin
layout: Enhance the heuristic that guesses the inline size of block
formatting contexts.

The widths of block formatting contexts depend on the floats prior to
them. To avoid a circular dependency between width assignment and height
assignment, we must guess their widths during the assign-widths pass.
The old code simply used the size of the last float, whether
left-floated or right-floated, but this proved insufficient to handle
layouts like those seen on Reddit. The new heuristic keeps track of both
left and right floats independently and sums the width of all left and
right floats to determine the width of a block formatting context. This
is still insufficient to properly lay out Reddit, but the results are
much more acceptable.

A fully correct approach will require that blocks be laid out again if
the initial guess proved to be incorrect. A `TODO` is in the code to
handle this case.
Merge pull request #3467 from pcwalton/enhance-block-formatting-context-guess

layout: Enhance the heuristic that guesses the inline size of block formatting contexts.

Reviewed-by: glennw
layout: Block formatting contexts should contain all their floats.

Improves Pinterest considerably.