Update Reading List icon

Changes the Reading List icon for the empty state with the new offline icon.

BUG=680152

Review-Url: https://codereview.chromium.org/2622003007
Cr-Commit-Position: refs/heads/master@{#443199}

ios/chrome/browser/ui/reading_list/BUILD.gn

@@ -10,9 +10,9 @@ bundle_data("resources") {
     "resources/distillation_success.png",
     "resources/distillation_success@2x.png",
     "resources/distillation_success@3x.png",
-    "resources/reading_list_icon.png",
-    "resources/reading_list_icon@2x.png",
-    "resources/reading_list_icon@3x.png",
+    "resources/reading_list_empty_state.png",
+    "resources/reading_list_empty_state@2x.png",
+    "resources/reading_list_empty_state@3x.png",
     "resources/reading_list_side_swipe.png",
     "resources/reading_list_side_swipe@2x.png",
     "resources/reading_list_side_swipe@3x.png",

ios/chrome/browser/ui/reading_list/reading_list_view_controller.mm

@@ -47,7 +47,7 @@
 
 namespace {
 
-NSString* const kEmptyReadingListBackgroundIcon = @"reading_list_icon";
+NSString* const kEmptyReadingListBackgroundIcon = @"reading_list_empty_state";
 NSString* const kBeginBoldMarker = @"BEGIN_BOLD_FONT";
 NSString* const kEndBoldMarker = @"END_BOLD_FONT";