[Custom Tabs] Implement "Read It Later" Behind a Flag

chrome/android/java/strings/android_chrome_strings.grd

Index: chrome/android/java/strings/android_chrome_strings.grd
diff --git a/chrome/android/java/strings/android_chrome_strings.grd b/chrome/android/java/strings/android_chrome_strings.grd
index 54d97a735106905629c1e7e72949dea69aeb48c0..99748f47bdd5b85cd81d026deab02cde2a4809c2 100644
--- a/chrome/android/java/strings/android_chrome_strings.grd
+++ b/chrome/android/java/strings/android_chrome_strings.grd
@@ -2272,6 +2272,14 @@ You are signing in with a managed account and giving its administrator control o
 However, you aren’t invisible. Going incognito doesn’t hide your browsing from your employer, your internet service provider, or the websites you visit.
       </message>
 
+      <!-- Custom tabs -->
+      <message name="IDS_READ_IT_LATER" desc="Text describing an option for the user to save the tab to Chrome and read it in the future.">
+        Read it later in Chrome
+      </message>
+      <message name="IDS_TAB_SENT_TO_BACKGROUND" desc="A message to show that the tab has been sent to the background Chrome.">
+        Your tab is now in the background.
+      </message>
+
       <!-- Contextual Search -->
       <message name="IDS_CONTEXTUAL_SEARCH_NETWORK_UNAVAILABLE" desc="Tells the user the network is not accessible.">
         Unable to access the network