Catch exception for Function.toString on Proxies etc.

[sbward]

Related to #568

Sometimes a Function Proxy gets inspected by getCustomFunctionDetails(), which breaks because Function.prototype.toString doesn't always work with Proxy objects.

This patch simply catches the TypeError and allows vue-devtools to continue rendering the Component details even if it contains funky Function Proxies. Currently if this occurs the Component detail view doesn't show, which leaves developers stuck tracking down the cause of the issue without the help of vue-devtools. This patch will at least allow the Component details to render, but the Function Proxy in question will not show argument details.

There might be a way to continue rendering the arguments for certain Function Proxies but I don't think it would be completely general.

[michalsnik]

Thanks for pointing and working on this @sbward.

I confirmed it, and the following code:

function sum(a, b) {
  return a + b;
}

const handler = {
  apply: function(target, thisArg, argumentsList) {
    console.log(`Calculate sum: ${argumentsList}`);
    return argumentsList[0] + argumentsList[1];
  }
};

const proxy1 = new Proxy(sum, handler);

Indeed produces an error:

// typeof proxy1 -> function
// Function.prototype.toString.call(proxy1) -> Function.prototype.toString requires that 'this' be a Function

I also don't see any other way of detecting if it's a proxy or not, so LGTM :)