Add "Keep chrome running in background" preference.

chrome/app/chromium_strings.grd

Index: chrome/app/chromium_strings.grd
diff --git a/chrome/app/chromium_strings.grd b/chrome/app/chromium_strings.grd
index a814f34243692050bd37261e51cd3b9618a384e4..c6d4c6a2f6dd58f9d9b09a91613c59e1cfb0c595 100644
--- a/chrome/app/chromium_strings.grd
+++ b/chrome/app/chromium_strings.grd
@@ -335,6 +335,12 @@ be available for now. -->
           Please sign out of Chromium OS and sign in again for this change to take effect.
         </message>
       </if>
+      <message name="IDS_OPTIONS_BACKGROUND_ENABLE_BACKGROUND_MODE" desc="The label of the check-box that enables background mode">
+        Continue running background apps when Chromium is closed

[Rick Campbell, 2011/05/11 20:33:01]

I think that you should replace "Continue running background apps when Chromium
is closed" with "Keep Chromium running in the background after the last window
is closed."

This phrasing revives points from older discussions, specifically (a) Chrome is
running, not just those apps and (b) "Chromium is closed" is not as
clear/correct as "last window closed."

[Andrew T Wilson (Slow), 2011/05/11 23:00:48]

My concern with the alternate wording is it sounds like checking the box would
keep chrome running in the background regardless of the presence of background
apps.

In any case, the strings I've added are basically verbatim from Jeff Chang's
email, and they'll go through UI review once I've landed this.

+      </message>
+      <message name="IDS_CONFIRM_EXIT_BACKGROUND_MODE_BODY" desc="Confirmation displayed when disabling background mode via the status tray context menu when there are no windows open">
+        Are you sure you want to quit Chromium? (This setting can be toggled in <ph name="OPTIONS_MENU_LABEL">$1<ex>Options</ex></ph> - Under the Hood)
+      </message>
       <message name="IDS_CANT_WRITE_USER_DIRECTORY_SUMMARY" desc="Summary of problem displayed in dialog when we can't create a directory for this user.">
         Chromium cannot read and write to its data directory:\n\n<ph name="USER_DATA_DIRECTORY">$1<ex>C:\Documents and Settings\devint\Local Settings\Application Data\Google\Chrome</ex></ph>
       </message>