Add guide for the omnibox popup on AdaptiveToolbar

This CL constrains the OmniboxLayoutGuide so it is positioned on the
omnibox of the adaptive toolbar.

Bug: 806248
Cq-Include-Trybots: master.tryserver.chromium.mac:ios-simulator-cronet;master.tryserver.chromium.mac:ios-simulator-full-configs
Change-Id: I84a19370868ff152402a6039c626acb28cc6a26c
Reviewed-on: https://chromium-review.googlesource.com/888640Reviewed-by: Louis Romero <lpromero@chromium.org>
Commit-Queue: Gauthier Ambard <gambard@chromium.org>
Cr-Commit-Position: refs/heads/master@{#532368}

ios/chrome/browser/ui/toolbar/adaptive/primary_toolbar_view_controller.mm

@@ -101,6 +101,11 @@
   [self addLongPressGestureToView:self.view.forwardTrailingButton];
 }
 
+- (void)didMoveToParentViewController:(UIViewController*)parent {
+  [super didMoveToParentViewController:parent];
+  ConstrainNamedGuideToView(kOmniboxGuide, self.view.locationBarContainer);
+}
+
 #pragma mark - Property accessors
 
 - (void)setLocationBarView:(UIView*)locationBarView {