Create private functions to do error messages in browser.ts

[cnishina]

Discussion and promise to do it in #5034 for the following

(line 655ish)

      if (timeout) {
        let errMsg = `Timed out waiting for asynchronous Angular tasks to finish after ` +
            `${timeout}. This may be because the current page is not an Angular ` +
            `application. Please see the FAQ for more details: ` +

and
(line 642ish)

      }, this.allScriptsTimeout, 'Plugins.waitForCondition()');
    } catch (err) {
      let timeout: RegExpExecArray;
      if (/asynchronous script timeout/.test(err.message)) {

[cnishina]

I'm not sure if there's a value add here. I would refactor by moving the error message out. It would make it a little more readable; however, this private method would only be used in one location. I am going to close this as a won't fix.