1571963 - Teach nsIFrame::Init() the type of continuation to create

Status: NEW

(Core :: Layout, task, P3)

Description

[Ting-Yu Lin [:TYLin] (PST, UTC-8)]

The concept of non-fluid (or fixed) continuations was added in bug 299065.

When calling nsCSSFrameConstructor::CreateContinuingFrame(), we does require the caller to pass aFluid to distinguish which kind of continuation to create. However, nsIFrame::Init() lacks such an argument, so it always creates a fluid continuation, and later it tweaks the continuation to be non-fluid.

What I'd like to do:

1. Add an extra argument to nsIFrame::Init() to indicate the type of continuation to create. The argument is better not to be a bool, but a strong type like enum class FrameContinuationTypes {Fluid, NonFluid}.
2. Move this tweak into nsSplittableFrame::Init and nsContinuingTextFrame::Init.
3. Audit the caller of nsCSSFrameConstructor::CreateContinuingFrame to use the enum class instead of aFluid.
4. Rename nsFrame::Init's parameter aPrevInFlow to aPrevContinuation as suggested by dbaron in https://phabricator.services.mozilla.com/D40761#1229155