Unify dart:html.{Rect,ClientRect,SVGRect}

[DartBot]

This issue was originally filed by @seaneagan

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dart:html has three different interfaces to represent a Rectangle:

Rect
ClientRect
SVGRect

These ought to be unified into a single interface. The dart style guide recommends not to use abbreviations, so ideally it would be named 'Rectangle' instead of just 'Rect'.

[DartBot]

This comment was originally written by antonm@google.com

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cc @rakudrama.
cc @vsmenon.
Added Area-DOM label.

[sethladd]

Removed Type-Defect label.
Added Type-Enhancement, Triaged labels.

[iposva-google]

Removed Area-DOM label.
Added Area-HTML label.

[rakudrama]

There is no field common to all three types.
ClientRect has 6 fields.
Rect has a subset, but they are CSSPrimitiveValues, not num-bers.
These types come from deep inside WekKit, so unifying them would require code to translate to and from the underlying representation.

I'm supportive of the general idea so we will revisit after M1 but I think it will turn out that these types are too different to unify.

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Added this to the Later milestone.

[efortuna]

putting as m7 to remind us to follow up with florian.

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Removed this from the Later milestone.
Added this to the M7 milestone.

[efortuna]

Set owner to @efortuna.

[efortuna]

Added Waiting label.

[blois]

Removed this from the M7 milestone.
Added this to the M8 milestone.

[efortuna]

In https://codereview.chromium.org//25808002 we moved Rectangle over to dart:math, and Client rect is merged with regular rect. SVG could probably be merged, but I'm postponing that part until a later milestone.

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Removed this from the M8 milestone.
Added this to the Later milestone.
Added Accepted label.

[kevmoo]

Removed Area-HTML label.
Added Area-Library, Library-Html labels.

[kasperl]

Removed this from the Later milestone.
Added Oldschool-Milestone-Later label.

[kasperl]

Removed Oldschool-Milestone-Later label.