Use a black bottom nav for SearchActivityTheme

BUG=

Change-Id: Ic2e4a9abe542e2ebce04ce89de7f3e77cb5eda13
Reviewed-on: https://chromium-review.googlesource.com/904950Reviewed-by: Ted Choc <tedchoc@chromium.org>
Commit-Queue: Theresa <twellington@chromium.org>
Cr-Commit-Position: refs/heads/master@{#534868}

chrome/android/java/res/values-v17/styles.xml

@@ -44,7 +44,9 @@
     </style>
     <style name="MainTheme" parent="MainThemeBase" />
 
-    <style name="SearchActivityTheme" parent="MainTheme">
+    <!-- Extend MainThemeBase rather than MainTheme to avoid values-v27 navigation bar colors from
+         being applied -->
+    <style name="SearchActivityTheme" parent="MainThemeBase">
         <item name="android:windowBackground">@color/google_grey_500</item>
     </style>