Fix select tag test race condition on Vega

Fixes a race condition in VrBrowserWebInputEditingTest#testSelectTag
on Vega (and probably other fast devices) where the click meant for the
modal dialog could happen so fast that it registered on the web contents
instead of the dialog, causing the dialog to be dismissed.

Bug: 876946
Change-Id: I043e19d49ce02e76de4b2447619f365e8dc90244
Reviewed-on: https://chromium-review.googlesource.com/c/1456940Reviewed-by: Bill Orr <billorr@chromium.org>
Commit-Queue: Brian Sheedy <bsheedy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#630022}

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

@@ -146,6 +146,11 @@ public class VrBrowserWebInputEditingTest {
         DOMUtils.clickNode(mVrBrowserTestFramework.getFirstTabWebContents(), "selectbox",
                 false /* goThroughRootAndroidView */);
         NativeUiUtils.waitForModalDialogStatus(true /* shouldBeShown */, mVrTestRule.getActivity());
+        // On fast devices such as the Vega, it's possible to send the first click before the modal
+        // dialog starts accepting any input, causing the click to be registered on the web contents
+        // and causing the dialog to be dismissed. So, ensure that the dialog is at least done
+        // rendering before trying to send input.
+        NativeUiUtils.waitForUiQuiescence();
         // Click on whichever option is near the center of the screen. We don't care which, as long
         // as it's not the initial selection, which should be at the top. Clicking in the exact
         // center can sometimes click in the area between two options, so offset slightly to prevent