Add dark action bar color to colors.xml

We want to use the same color between Chrome and an external activity in
GMS core, and we can launch this activity with a custom color, so this change
makes the color accessible in both places.

BUG=480598

Review URL: https://codereview.chromium.org/1136953008

Cr-Commit-Position: refs/heads/master@{#329324}

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

@@ -96,7 +96,7 @@
     <style name="ThemeWithActionBar" parent="Theme.AppCompat.Light.DarkActionBar">
         <item name="android:windowBackground">@drawable/action_bar_activity_bg</item>
         <!-- Action bar color -->
-        <item name="colorPrimary">#263238</item>
+        <item name="colorPrimary">@color/dark_action_bar_color</item>
         <!-- Status bar color -->
         <item name="colorPrimaryDark">#161e21</item>
         <!-- Color of checkboxes, switches, buttons, etc. -->

chrome/android/java/res/values/colors.xml

@@ -13,6 +13,7 @@
     <color name="input_underline_error_color">#d32f2f</color>
     <color name="explanation_text_color">#909090</color>
     <color name="text_highlight_color">#C6DAFC</color>
+    <color name="dark_action_bar_color">#263238</color>
 
     <!-- Infobar colors -->
     <color name="infobar_background">#fff</color>