function setCurrentContext(ctx) {
    if (ctx != currentContext ||
        ctx.drawingBufferWidth != currentContextWidth ||
        ctx.drawingBufferHeight != currentContextHeight) {
      currentContext = ctx;
      currentContextWidth = ctx.drawingBufferWidth;
      currentContextHeight = ctx.drawingBufferHeight;
      setContextEvent(
          getHandle(ctx),
          ctx.drawingBufferWidth, ctx.drawingBufferHeight);
    }
  }
Injects the WebGLRenderingContext proto instrumentation.
@private