Optimize contexts for reading frequently

This was a recommendation from Edge.
Docs here: https://html.spec.whatwg.org/multipage/canvas.html#concept-canvas-will-read-frequently

src/browser/ColorManager.ts

@@ -89,7 +89,9 @@ export class ColorManager implements IColorManager {
     const canvas = document.createElement('canvas');
     canvas.width = 1;
     canvas.height = 1;
-    const ctx = canvas.getContext('2d');
+    const ctx = canvas.getContext('2d', {
+      willReadFrequently: true
+    });
     if (!ctx) {
       throw new Error('Could not get rendering context');
     }