Add XR test workaround for loadUrl

Adds a workaround for an issue where loadUrl was returning before loaded
scripts finished executing during XR tests, causing test flakiness. The
workaround changes the condition being checked to include a check that
the function being polled actually exists.

Bug: 894796
Change-Id: I080345688a6a268b2dda656f39a7e91523b2cb95
Reviewed-on: https://chromium-review.googlesource.com/c/1306173Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Brian Sheedy <bsheedy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#604308}

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

@@ -395,9 +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.
         Assert.assertTrue("Timed out waiting for JavaScript test initialization",
-                pollJavaScriptBoolean("isInitializationComplete()", POLL_TIMEOUT_LONG_MS,
-                        mRule.getWebContents()));
+                pollJavaScriptBoolean("isInitializationComplete && isInitializationComplete()",
+                        POLL_TIMEOUT_LONG_MS, mRule.getWebContents()));
         return result;
     }