[ChromeDriver] Modify condition for turning off W3C mode

Previously, W3C mode would be turned off if no capabilities were found.
This changelist changes this behavior so that W3C mode is turned off if
both no capabilities are found and there exists desiredCapabilities. This
change is necessary to be W3C compliant as the change allows two WPT tests
to pass: test_no_capabilities and test_desired

R=johnchen@chromium.org

Bug: chromedriver:3013
Change-Id: I8c088bd0a15cd3be9a0a41e80fdc4c40808fa0a7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1698862Reviewed-by: John Chen <johnchen@chromium.org>
Commit-Queue: Julian Kung <juliankung@google.com>
Cr-Commit-Position: refs/heads/master@{#676647}

chrome/test/chromedriver/session_commands.cc

@@ -111,7 +111,7 @@ bool GetW3CSetting(const base::DictionaryValue& params) {
     }
   }
 
-  if (!params.HasKey("capabilities")) {
+  if (!params.HasKey("capabilities") && params.HasKey("desiredCapabilities")) {
     return false;
   }