Change assign to copy for block property

RecentTabsHandsetCoordinator should retain its block property.

Bug: 775508
Change-Id: Ifd9bd829786592adde9057bec68bf3a73b6c9fc2
Reviewed-on: https://chromium-review.googlesource.com/723304
Reviewed-by: Jean-François Geyelin <[email protected]>
Commit-Queue: Gauthier Ambard <[email protected]>
Cr-Original-Commit-Position: refs/heads/master@{#509383}(cherry picked from commit 51058e6)
Reviewed-on: https://chromium-review.googlesource.com/726119
Reviewed-by: Gauthier Ambard <[email protected]>
Cr-Commit-Position: refs/branch-heads/3239@{#51}
Cr-Branched-From: adb61db-refs/heads/master@{#508578}

Author: Gauthier Ambard

ios/chrome/browser/ui/ntp/recent_tabs/recent_tabs_handset_coordinator.mm

@@ -20,7 +20,7 @@ @interface RecentTabsHandsetCoordinator ()<
     RecentTabsHandsetViewController* recentTabsViewController;
 @property(nonatomic, strong) RecentTabsTableCoordinator* tableCoordinator;
 // Completion block called once the recentTabsViewController is dismissed.
-@property(nonatomic, assign) ProceduralBlock completion;
+@property(nonatomic, copy) ProceduralBlock completion;
 
 @end