Drop Image data once rendered

Helps the browser to free up the memory right away, rather than waiting
until some later cleanup process. At least Firefox can start consuming
gigabytes of memory without this.

Author: CendioOssman

core/display.js

@@ -521,6 +521,9 @@ export default class Display {
                             return;
                         }
                         this.drawImage(a.img, a.x, a.y);
+                        // This helps the browser free the memory right
+                        // away, rather than ballooning
+                        a.img.src = "";
                     } else {
                         a.img._noVNCDisplay = this;
                         a.img.addEventListener('load', this._resumeRenderQ);

tests/test.display.js

@@ -384,10 +384,11 @@ describe('Display/Canvas helper', function () {
         });
 
         it('should draw an image from an image object on type "img" (if complete)', function () {
+            const img = { complete: true };
             display.drawImage = sinon.spy();
-            display._renderQPush({ type: 'img', x: 3, y: 4, img: { complete: true } });
+            display._renderQPush({ type: 'img', x: 3, y: 4, img: img });
             expect(display.drawImage).to.have.been.calledOnce;
-            expect(display.drawImage).to.have.been.calledWith({ complete: true }, 3, 4);
+            expect(display.drawImage).to.have.been.calledWith(img, 3, 4);
         });
     });
 });