9ff564d485
`PresShell::GetRootScrollFrameAsScrollable()` is equivalent to `PresShell::GetRootScrollContainerFrame()`. In ScrollContainerFrame.h, `DecideScrollableLayer()` has two versions, one has four parameters, and the other has five parameters with the fifth parameter `aDirtyRectHasBeenOverriden` having a default value `nullptr`. When we switch the caller from `nsIScrollableFrame` to `ScrollContainerFrame`, we need to remove the default value for the fifth parameter to avoid ambiguity. Differential Revision: https://phabricator.services.mozilla.com/D211494