This migrates TextNode::text_for_rendering() to Utf16String and deals
with the fallout. As a consequence, this effectively reverts commit
3df83dade8.
The layout test expecation file updates are because we now express text
lengths and offsets in UTF-16 code units.
The selection-over-multiple-code-units expectation file update actually
represents a correctness fix. Our result now matches Firefox.
Browsers such as Chrome and Firefox apply an arbitrary scale to the
current font size if `normal` is used for `line-height`. Firefox uses
1.2 while Chrome uses 1.15. Let's go with the latter for now, it's
relatively easy to change if we ever want to go back on that decision.
This also requires updating the expectations for a lot of layout tests.
The upside of this is that it's a bit easier to compare our layout
results to other browsers', especially Chrome.
When traversing the layout tree to find an appropriate box child to
derive the baseline from. Only the child's margin and offset was being
applied. Now we sum each offset on the recursive call.
This is a part of refactoring towards making the paintable tree
independent of the layout tree. Now, instead of transferring text
fragments from the layout tree to the paintable tree during the layout
commit phase, we allocate separate PaintableFragments that contain only
the information necessary for painting. Doing this also allows us to
get rid LineBoxes, as they are used only during layout.
This patch makes a few changes to the way we calculate line-height:
- `line-height: normal` is now resolved using metrics from the used
font (specifically, round(A + D + lineGap)).
- `line-height: calc(...)` is now resolved at style compute time.
- `line-height` values are now absolutized at style compute time.
As a consequence of the above, we no longer need to walk the DOM
ancestor chain looking for line-heights during style computation.
Instead, values are inherited, resolved and absolutized locally.
This is not only much faster, but also makes our line-height metrics
match those of other engines like Gecko and Blink.
If an element is created from JS, it might have its contents modified
before it is inserted into the document. In this case, we don't have a
shadow tree yet and so trying to set m_text_node's text content would
cause a null dereference. So let's not do that. :^)
That case also means that by the time we do create the shadow tree, we
have the text content already, so we can set it there.
Added a test to verify that we don't crash, and that the text content
appears in the textarea whether it was inserted by JS or by the HTML
parser.
