Auto merge of #21826 - servo:jdm-patch-35, r=jdm

Enable fake fillText API in nightly builds.

The [three.js examples](https://threejs.org/examples/) are really useful for checking Servo WebGL support, but if the fillText API is not available they only display a blank screen. I think it's worth lying to web content about this API in order to make it easy to make use of these examples without using local development builds.

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resources/prefs.json

@@ -1,7 +1,7 @@
 {
   "dom.bluetooth.enabled": false,
   "dom.bluetooth.testing.enabled": false,
-  "dom.canvas-text.enabled": false,
+  "dom.canvas-text.enabled": true,
   "dom.compositionevent.enabled": false,
   "dom.customelements.enabled": true,
   "dom.forcetouch.enabled": false,

tests/wpt/metadata/2dcontext/__dir__.ini

@@ -0,0 +1 @@
+prefs: ["dom.canvas-text.enabled:false"]

tests/wpt/metadata/html/dom/interfaces.https.html.ini

@@ -4259,9 +4259,6 @@
   [CanvasRenderingContext2D interface: operation scrollPathIntoView(Path2D)]
     expected: FAIL
 
-  [CanvasRenderingContext2D interface: operation fillText(DOMString, unrestricted double, unrestricted double, unrestricted double)]
-    expected: FAIL
-
   [CanvasRenderingContext2D interface: operation strokeText(DOMString, unrestricted double, unrestricted double, unrestricted double)]
     expected: FAIL
 
@@ -4334,12 +4331,6 @@
   [CanvasRenderingContext2D interface: calling scrollPathIntoView(Path2D) on document.createElement("canvas").getContext("2d") with too few arguments must throw TypeError]
     expected: FAIL
 
-  [CanvasRenderingContext2D interface: document.createElement("canvas").getContext("2d") must inherit property "fillText(DOMString, unrestricted double, unrestricted double, unrestricted double)" with the proper type]
-    expected: FAIL
-
-  [CanvasRenderingContext2D interface: calling fillText(DOMString, unrestricted double, unrestricted double, unrestricted double) on document.createElement("canvas").getContext("2d") with too few arguments must throw TypeError]
-    expected: FAIL
-
   [CanvasRenderingContext2D interface: document.createElement("canvas").getContext("2d") must inherit property "strokeText(DOMString, unrestricted double, unrestricted double, unrestricted double)" with the proper type]
     expected: FAIL
 
@@ -10292,9 +10283,6 @@
   [CanvasRenderingContext2D interface: operation scrollPathIntoView(Path2D)]
     expected: FAIL
 
-  [CanvasRenderingContext2D interface: operation fillText(DOMString, unrestricted double, unrestricted double, unrestricted double)]
-    expected: FAIL
-
   [CanvasRenderingContext2D interface: operation strokeText(DOMString, unrestricted double, unrestricted double, unrestricted double)]
     expected: FAIL
 
@@ -10367,12 +10355,6 @@
   [CanvasRenderingContext2D interface: calling scrollPathIntoView(Path2D) on document.createElement("canvas").getContext("2d") with too few arguments must throw TypeError]
     expected: FAIL
 
-  [CanvasRenderingContext2D interface: document.createElement("canvas").getContext("2d") must inherit property "fillText(DOMString, unrestricted double, unrestricted double, unrestricted double)" with the proper type]
-    expected: FAIL
-
-  [CanvasRenderingContext2D interface: calling fillText(DOMString, unrestricted double, unrestricted double, unrestricted double) on document.createElement("canvas").getContext("2d") with too few arguments must throw TypeError]
-    expected: FAIL
-
   [CanvasRenderingContext2D interface: document.createElement("canvas").getContext("2d") must inherit property "strokeText(DOMString, unrestricted double, unrestricted double, unrestricted double)" with the proper type]
     expected: FAIL