[canvaskit] Add API for deleting webgl ctx

Change-Id: I55e70cc1ae6b16d642dd63170e9402bd3c192d5f
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/343101
Reviewed-by: Nathaniel Nifong <nifong@google.com>

modules/canvaskit/CHANGELOG.md

@@ -8,6 +8,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Added
  - `getImageInfo()` and `getColorSpace()` to the `Image` type.
+ - `CanvasKit.deleteContext` for deleting WebGL contexts when done with them, resizing, etc.
 
 ### Breaking
  - `Path.addPoly()` no longer accepts a 2d array of points, but a flattened 1d array.

modules/canvaskit/canvaskit/types/canvaskit-wasm-tests.ts

@@ -344,6 +344,7 @@ function fontMgrTests(CK: CanvasKit) {
 function globalTests(CK: CanvasKit) {
     const ctx = CK.currentContext();
     CK.setCurrentContext(ctx);
+    CK.deleteContext(ctx);
     const n = CK.getDecodeCacheLimitBytes();
     const u = CK.getDecodeCacheUsedBytes();
     CK.setDecodeCacheLimitBytes(1000);

modules/canvaskit/canvaskit/types/index.d.ts

@@ -263,6 +263,12 @@ export interface CanvasKit {
      */
     setCurrentContext(ctx: WebGLContextHandle): void;
 
+    /**
+     * Deletes the associated WebGLContext. Function not available on the CPU version.
+     * @param ctx
+     */
+    deleteContext(ctx: WebGLContextHandle): void;
+
     /**
      * Returns the max size of the global cache for bitmaps used by CanvasKit.
      */

modules/canvaskit/externs.js

@@ -62,6 +62,7 @@ var CanvasKit = {
   Free: function() {},
   computeTonalColors: function() {},
   currentContext: function() {},
+  deleteContext: function() {},
   getColorComponents: function() {},
   getDecodeCacheLimitBytes: function() {},
   getDecodeCacheUsageBytes: function() {},
@@ -72,7 +73,7 @@ var CanvasKit = {
   setDecodeCacheLimitBytes: function() {},
 
   // Defined by emscripten.
-  createContext:function() {},
+  createContext: function() {},
 
   // private API (i.e. things declared in the bindings that we use
   // in the pre-js file)

modules/canvaskit/gpu.js

@@ -48,7 +48,11 @@
         }
         GL.makeContextCurrent(handle);
         return handle;
-      }
+      };
+
+      CanvasKit.deleteContext = function(handle) {
+        GL.deleteContext(handle);
+      };
 
       // idOrElement can be of types:
       //  - String - in which case it is interpreted as an id of a