Previously layout was exiting early because the frame view
was null. Now we actually compute some layout and paint the
text. This patch makes paragraph_builder_test pass.
Rather than using the DOM to upload text and styling information into the
engine, this patch begins sketching a more direct API that bypasses the DOM and
CSS. Currently, this API doesn't do anything, but it's a first step.
The approach is to have a ParagraphBuilder object that can record a tree of
style interior nodes and text leaves. The build() function then applies
container-level styling information (such as TextAlign) and returns a Paragraph
object that can undergo layout and paint.
The inputs to the builder process are immutable style objects constructed from
primitive values. These primitives are currently carbon-copies of the primitive
we use in the framework today. After this patch lands, I'll convert the frame
to re-expose these values instead of re-defining them.
