Auto merge of #24261 - paulrouget:fakeMeasureTExt, r=jdm

Temporary implementation of Canvas.MeasureText

@jdm: that will help with the babylonjs demos. Another approach is to implement that in JS and add it to the demos.

<!-- Reviewable:start -->
---
This change is [<img src="https://reviewable.io/review_button.svg" height="34" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/servo/24261)
<!-- Reviewable:end -->

1 files changed, 23 insertions, 0 deletions

diff --git a/components/script/dom/webidls/TextMetrics.webidl b/components/script/dom/webidls/TextMetrics.webidl
new file mode 100644
index 00000000000..f3d90450824
--- /dev/null
+++ b/components/script/dom/webidls/TextMetrics.webidl
@@ -0,0 +1,23 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
+
+// https://html.spec.whatwg.org/multipage/#textmetrics
+[Exposed=(PaintWorklet, Window, Worker), Pref="dom.canvas-text.enabled"]
+interface TextMetrics {
+  // x-direction
+  readonly attribute double width; // advance width
+  readonly attribute double actualBoundingBoxLeft;
+  readonly attribute double actualBoundingBoxRight;
+
+  // y-direction
+  readonly attribute double fontBoundingBoxAscent;
+  readonly attribute double fontBoundingBoxDescent;
+  readonly attribute double actualBoundingBoxAscent;
+  readonly attribute double actualBoundingBoxDescent;
+  readonly attribute double emHeightAscent;
+  readonly attribute double emHeightDescent;
+  readonly attribute double hangingBaseline;
+  readonly attribute double alphabeticBaseline;
+  readonly attribute double ideographicBaseline;
+};