Omnibox: Set color right after restart

Omnibox is getting Tab instance from LayoutManager to find the right
color for its background. After restart (by forcing-stop Chrome or
by changing theme), however, LayoutManager was not setting the current
Tab instance properly. This CL ensures it is done in the initialization
step.

Bug: 1108235
Change-Id: I3445e6c8b9de6bcb7582a42bd0544b05fbfe00b8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2315463Reviewed-by: Matthew Jones <mdjones@chromium.org>
Commit-Queue: Jinsuk Kim <jinsukkim@chromium.org>
Cr-Commit-Position: refs/heads/master@{#791674}

chrome/android/java/src/org/chromium/chrome/browser/compositor/layouts/LayoutManager.java

@@ -457,6 +457,7 @@ public class LayoutManager implements LayoutUpdateHost, LayoutProvider,
     public void setTabModelSelector(TabModelSelector selector) {
         mTabModelSelector = selector;
         mTabModelSelectorSupplier.set(selector);
+        mCurrentTab = selector.getCurrentTab();
         mTabModelSelectorTabObserver = new TabModelSelectorTabObserver(mTabModelSelector) {
             @Override
             public void onShown(Tab tab, @TabSelectionType int type) {