[AW][Dev-UI] adjust flag UI colors

No change to logic. This adjusts the following colors:

* Brighter red for warning text (dark theme only)
* More contrast for text color of flag names (darker in light theme,
  brighter in dark theme)

Fixed: 1111172
Test: Manual - verify colors in screenshot
Change-Id: Ib8d1e5a8cbd10c8b7e3483adb31c893d220389f2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2347376Reviewed-by: Hazem Ashmawy <hazems@chromium.org>
Commit-Queue: Nate Fischer <ntfschr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#797027}

android_webview/nonembedded/java/res_devui/layout/toggleable_flag.xml

@@ -19,7 +19,7 @@
         android:layout_height="wrap_content"
         android:textIsSelectable="true"
         android:textStyle="bold"
-        android:textAppearance="?android:attr/textAppearanceMedium"
+        android:textAppearance="@style/MediumText"
         android:drawablePadding="4dp"
         android:paddingTop="8dp"
         android:paddingBottom="8dp"/>

android_webview/nonembedded/java/res_devui/values-night/colors.xml

@@ -6,5 +6,7 @@
 -->
 
 <resources>
+    <color name="error_red">#F28482</color>
     <color name="navigation_selected">#FFFFFF</color>
+    <color name="medium_text_color">#E8EAED</color>
 </resources>

android_webview/nonembedded/java/res_devui/values/colors.xml

@@ -11,4 +11,5 @@
     <color name="blue">#1967D2</color>
     <color name="navigation_selected">#000000</color>
     <color name="navigation_unselected">#888888</color>
+    <color name="medium_text_color">#202124</color>
 </resources>

android_webview/nonembedded/java/res_devui/values/styles.xml

@@ -13,4 +13,7 @@
     <style name="UnselectedNavigationButton">
         <item name="android:textColor">@color/navigation_unselected</item>
     </style>
+    <style name="MediumText" parent="@android:style/TextAppearance.Medium">
+        <item name="android:textColor">@color/medium_text_color</item>
+    </style>
 </resources>
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