[vr] Fix XR test workaround for loadUrl

The existing XR test workaround (crrev.com/c/1306173) checks for the
existence of isInitializationComplete by attempting to access it.
However, accessing an undeclared variable throws a ReferenceError -- the
correct way of checking for its existence is using typeof.

Bug: 894796
Change-Id: I86a5ac2ba45fea5e51c7e0f9fddc4167b8772443
Reviewed-on: https://chromium-review.googlesource.com/c/1319715Reviewed-by: Brian Sheedy <bsheedy@chromium.org>
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/master@{#605771}

chrome/android/javatests/src/org/chromium/chrome/browser/vr/XrTestFramework.java

@@ -395,10 +395,11 @@ public abstract class XrTestFramework {
     public int loadUrlAndAwaitInitialization(String url, int timeoutSec)
             throws InterruptedException {
         int result = mRule.loadUrl(url, timeoutSec);
-        // TODO(https://crbug.com/894796): Remove the first isInitializationComplete once loadUrl
-        // is fixed.
+        // TODO(https://crbug.com/894796): Remove the isInitializationComplete undefined check once
+        // loadUrl is fixed.
         Assert.assertTrue("Timed out waiting for JavaScript test initialization",
-                pollJavaScriptBoolean("isInitializationComplete && isInitializationComplete()",
+                pollJavaScriptBoolean("(typeof isInitializationComplete !== 'undefined') && "
+                                + "isInitializationComplete()",
                         POLL_TIMEOUT_LONG_MS, mRule.getWebContents()));
         return result;
     }