Update getCurrentTexture test to match spec.

It's not entirely clear from the current WebGPU spec if "modified" = setting
to the same dimensions. It seems like that shouldn't matter and is inconsistent with
other canvas contents.

src/webgpu/web_platform/canvas/getCurrentTexture.spec.ts

@@ -40,6 +40,27 @@ class GPUContextTest extends GPUTest {
 
     return ctx;
   }
+
+  expectTextureDestroyed(texture: GPUTexture, expectDestroyed = true) {
+    this.expectValidationError(() => {
+      // Try using the texture in a render pass. Because it's a canvas texture
+      // it should have RENDER_ATTACHMENT usage.
+      assert((texture.usage & GPUTextureUsage.RENDER_ATTACHMENT) !== 0);
+      const encoder = this.device.createCommandEncoder();
+      const pass = encoder.beginRenderPass({
+        colorAttachments: [
+          {
+            view: texture.createView(),
+            loadOp: 'clear',
+            storeOp: 'store',
+          },
+        ],
+      });
+      pass.end();
+      // Submitting should generate a validation error if the texture is destroyed.
+      this.queue.submit([encoder.finish()]);
+    }, expectDestroyed);
+  }
 }
 
 export const g = makeTestGroup(GPUContextTest);
@@ -235,6 +256,8 @@ g.test('resize')
     // Trigger a resize by changing the width.
     ctx.canvas.width = 4;
 
+    t.expectTextureDestroyed(prevTexture);
+
     // When the canvas resizes the texture returned by getCurrentTexture should immediately begin
     // returning a new texture matching the update dimensions.
     let currentTexture = ctx.getCurrentTexture();
@@ -263,21 +286,35 @@ g.test('resize')
     t.expect(currentTexture.height === ctx.canvas.height);
     t.expect(prevTexture.width === 4);
     t.expect(prevTexture.height === 2);
-    prevTexture = currentTexture;
 
     // Ensure that texture contents are transparent black.
     t.expectSingleColor(currentTexture, currentTexture.format, {
       size: [currentTexture.width, currentTexture.height, 1],
       exp: { R: 0, G: 0, B: 0, A: 0 },
     });
 
-    // Simply setting the canvas width and height values to their current values should not trigger
-    // a change in the texture.
-    ctx.canvas.width = 4;
-    ctx.canvas.height = 4;
+    // Ensure canvas goes back to defaults when set to negative numbers.
+    ctx.canvas.width = -1;
+    currentTexture = ctx.getCurrentTexture();
+    t.expect(currentTexture.width === 300);
+    t.expect(currentTexture.height === 4);
 
+    ctx.canvas.height = -1;
     currentTexture = ctx.getCurrentTexture();
-    t.expect(prevTexture === currentTexture);
+    t.expect(currentTexture.width === 300);
+    t.expect(currentTexture.height === 150);
+    prevTexture = currentTexture;
+
+    // Setting the canvas width and height values to their current values should
+    // still trigger a change in the texture.
+    const { width, height } = ctx.canvas;
+    ctx.canvas.width = width;
+    ctx.canvas.height = height;
+
+    t.expectTextureDestroyed(prevTexture);
+
+    currentTexture = ctx.getCurrentTexture();
+    t.expect(prevTexture !== currentTexture);
   });
 
 g.test('expiry')