[Android] Photo Picker: Fix Zoom icon background in Dark mode.

This CL adds a circular background to the Zoom icons (on top of
the navigation_bubble_shadow). The circular background supports
Dark mode (is gray when Dark mode is enabled, and white when not).

Bug: 656015
Change-Id: Ibf91c607add40be77807b88f66a7ed82f2955266
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1959031
Commit-Queue: Finnur Thorarinsson <finnur@chromium.org>
Auto-Submit: Finnur Thorarinsson <finnur@chromium.org>
Reviewed-by: Boris Sazonov <bsazonov@chromium.org>
Cr-Commit-Position: refs/heads/master@{#723392}

chrome/android/java/res/drawable/zoom_in.xml

@@ -9,6 +9,9 @@
     android:viewportWidth="24"
     android:viewportHeight="24">
 
+    <path
+        android:fillColor="@color/modern_primary_color"
+        android:pathData="M0 12a12 12 0 1 1 24 0a12 12 0 1 1 -24 0"/>
     <path
         android:fillColor="@color/default_icon_color"
         android:pathData="M 14.625 13.5 L 14.033 13.5 L 13.822 13.297 C 14.557 12.443 15 11.332 15 10.125 C 15 7.433 12.818 5.25 10.125 5.25 C 7.433 5.25 5.25 7.433 5.25 10.125 C 5.25 12.818 7.433 15 10.125 15 C 11.332 15 12.443 14.557 13.297 13.822 L 13.5 14.033 L 13.5 14.625 L 17.25 18.367 L 18.367 17.25 L 14.625 13.5 Z M 10.125 13.5 C 8.258 13.5 6.75 11.992 6.75 10.125 C 6.75 8.258 8.258 6.75 10.125 6.75 C 11.992 6.75 13.5 8.258 13.5 10.125 C 13.5 11.992 11.992 13.5 10.125 13.5 Z"/>

chrome/android/java/res/drawable/zoom_out.xml

@@ -9,6 +9,9 @@
     android:viewportWidth="24"
     android:viewportHeight="24">
 
+    <path
+        android:fillColor="@color/modern_primary_color"
+        android:pathData="M0 12a12 12 0 1 1 24 0a12 12 0 1 1 -24 0"/>
     <path
         android:pathData="M 3 3 L 21 3 L 21 21 L 3 21 L 3 3 Z"/>
     <path