[canvaskit] missing extern

Bug: skia:
Change-Id: I9893650b394c71ced15c0b6b7623a4c3081cedff
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/201225
Reviewed-by: Kevin Lubick <kjlubick@google.com>

modules/canvaskit/CHANGELOG.md

@@ -9,6 +9,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Changed
  - Location in Skia Git repo now `modules/canvaskit` (was `experimental/canvaskit`)
 
+### Fixed
+ - Extern bug in `CanvasKit.SkMatrix.invert`
+
 ## [0.5.0] - 2019-03-08
 
 ### Added

modules/canvaskit/externs.js

@@ -160,6 +160,7 @@ var CanvasKit = {
 
 	SkMatrix: {
 		identity: function() {},
+		invert: function() {},
 		mapPoints: function() {},
 		multiply: function() {},
 		rotated: function() {},