Auto merge of #14367 - mrobinson:scroll-fragment-point, r=pcwalton

Reimplement scrolling to fragments

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- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes fix #13736, #10753 (github issue number if applicable).

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- [x] There are tests for these changes OR
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This reimplemntation of the feature uses ScrollRootIds to scroll
particular scrollable areas of the page.

Fixes #13736.
Fixes #10753.

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components/script_traits/script_msg.rs

@@ -16,6 +16,7 @@ use canvas_traits::CanvasMsg;
 use devtools_traits::{ScriptToDevtoolsControlMsg, WorkerId};
 use euclid::point::Point2D;
 use euclid::size::Size2D;
+use gfx_traits::ScrollRootId;
 use ipc_channel::ipc::IpcSender;
 use msg::constellation_msg::{FrameId, PipelineId, TraversalDirection};
 use msg::constellation_msg::{Key, KeyModifiers, KeyState};
@@ -121,7 +122,7 @@ pub enum ScriptMsg {
     /// Check if an alert dialog box should be presented
     Alert(PipelineId, String, IpcSender<bool>),
     /// Scroll a page in a window
-    ScrollFragmentPoint(PipelineId, Point2D<f32>, bool),
+    ScrollFragmentPoint(PipelineId, ScrollRootId, Point2D<f32>, bool),
     /// Set title of current page
     /// https://html.spec.whatwg.org/multipage/#document.title
     SetTitle(PipelineId, Option<String>),