MD Settings: allow changing to GTK+ theme on Linux

chrome/app/settings_strings.grdp

Index: chrome/app/settings_strings.grdp
diff --git a/chrome/app/settings_strings.grdp b/chrome/app/settings_strings.grdp
index 0f6574bed9601a51b3ac014a6abba2e650bd928b..839ac3d63aa2e7db4c96a1ca59e8e761a57e71c4 100644
--- a/chrome/app/settings_strings.grdp
+++ b/chrome/app/settings_strings.grdp
@@ -177,12 +177,28 @@
   <message name="IDS_SETTINGS_SET_WALLPAPER" desc="Name of the control which allows the user to set the wallpaper.">
     Wallpaper
   </message>
-  <message name="IDS_SETTINGS_THEME" desc="Name of the control which allows the user to get a theme for the browser.">
-    Theme
-  </message>
-  <message name="IDS_SETTINGS_RESET_TO_DEFAULT_THEME" desc="Name of the control which resets the browser theme back to the default theme.">
-    Reset to default
+  <message name="IDS_SETTINGS_THEMES" desc="Name of the control which allows the user to get a theme for the browser.">
+    Themes
   </message>
+  <if expr="is_linux and not chromeos">
+    <message name="IDS_SETTINGS_SYSTEM_THEME" desc="Text of the label describing the system (GTK+) browser theme on Linux">
+      GTK+
+    </message>
+    <message name="IDS_SETTINGS_USE_SYSTEM_THEME" desc="Text of the button that switches the browser theme to the system (GTK+) theme on Linux">
+      Use GTK+
+    </message>
+    <message name="IDS_SETTINGS_CLASSIC_THEME" desc="Text of the label describing the classic browser theme on Linux">
+      Classic
+    </message>
+    <message name="IDS_SETTINGS_USE_CLASSIC_THEME" desc="Text of the button that switches the browser theme to the classic theme on Linux">
+      Use Classic
+    </message>
+  </if>
+  <if expr="not is_linux or chromeos">
+    <message name="IDS_SETTINGS_RESET_TO_DEFAULT_THEME" desc="Name of the control which resets the browser theme back to the default theme.">
+      Reset to default
+    </message>
+  </if>
   <message name="IDS_SETTINGS_SHOW_HOME_BUTTON" desc="Label for the checkbox which enables or disables showing the home button in the toolbar.">
     Show home button
   </message>