Wait to dump flow tree until flow is complete

The flow tree is currently dumped for debugging purposes early on in
the flow process, so many values are still zero. If we wait to dump it
until later, the output will more accurately reflect the real flow tree.
auto merge of #3719 : mrobinson/servo/flow-dump, r=pcwalton

The flow tree is currently dumped for debugging purposes early on in
the flow process, so many values are still zero. If we wait to dump it
until later, the output will more accurately reflect the real flow tree.
Edits dom/bindings/DESIGN.md

This corrects and improves the dom/bindings/DESIGN.md document and also
corrects a grammatical error in a tests/reftest.rs message.
auto merge of #3720 : gilles-leblanc/servo/fix-grammatical-errors, r=jdm

This corrects and improves the dom/bindings/DESIGN.md document and also
corrects a grammatical error in a tests/reftest.rs message.
Don't crash on invalid utf-8 in the HTML parser.

This was regressed by the html5ever landing.
auto merge of #3712 : Ms2ger/servo/parser-crash, r=Manishearth

This was regressed by the html5ever landing.
Fixes the table_percentage_width_a.html reftest with incremental reflow turned on.