title: Fetch inside content script fails with chrome-extension://invalid
body: <p>Inside my content script, I resolve a URL and execute a <code>fetch</code> on it:</p>
  <pre><code>let url = chrome.runtime.getURL('/hints/heart.html')
  
  console.log(&quot;url = &quot; + url)
  
  fetch(url)
      .then(r =&gt; r.text())
      .then(injectedContent =&gt; {
          // do stuff with injectedContent
      });
  </code></pre>
  <p>The URL is resolved correctly. I can see that from printing it to the console. The file there also exists.</p>
  <p>However, <code>fetch</code> is returning an error saying that it's trying to call the URL <code>chrome-extension://invalid</code>.</p>
  <p>I already added the path the <code>web_accessible_resource</code> in the manifest:</p>
  <pre><code>&quot;web_accessible_resources&quot;: [
      {
        &quot;resources&quot;: [ &quot;/hints/*&quot; ],
        &quot;matches&quot;: [ &quot;https://*.myurl.com/*&quot; ]
      }
    ]
  </code></pre>
  <p>What am I missing?</p>