title: Start a chromedriver session using w3c webdriver api
body: <p>I'm trying to start a Chromium session using the chromedriver and w3c webdriver API, I send a POST request to <code>http://localhost:9515/session</code> with the body</p>
  
  <pre><code>{
      "capabilities": {
          "alwaysMatch": {
              "platformName": "linux",
              "chrome:browserOptions": {
                  "binary": "/usr/bin/chromium",
                  "args": ["--start-page=about:blank"]
              }
          },
          "firstMatch": [
              {"browserName": "chrome"}
          ]
      }
  }
  </code></pre>
  
  <p>And i get the next response</p>
  
  <pre><code>{
      "sessionId": "b1a413df152017cd223dbabbcf1d2ffe",
      "status": 33,
      "value": {
          "message": "session not created exception: Missing or invalid capabilities (Driver info: chromedriver=2.40.565383 (76257d1ab79276b2d53ee976b2c3e3b9f335cde7),platform=Linux 4.14.47-1-MANJARO x86_64)"
      }
  }
  </code></pre>
  
  <p>Which capabilities are missing or invalid?</p>