Prevent a crash in TaskManagerWindowController by nil-ing the dataSource and delegate in dealloc.

chrome/browser/cocoa/task_manager_mac.mm

Index: chrome/browser/cocoa/task_manager_mac.mm
diff --git a/chrome/browser/cocoa/task_manager_mac.mm b/chrome/browser/cocoa/task_manager_mac.mm
index b4cee6673715ea86fd96224e36db1c591dac01a3..65241d2e604142c313e622ea33fe690c5df3f884 100644
--- a/chrome/browser/cocoa/task_manager_mac.mm
+++ b/chrome/browser/cocoa/task_manager_mac.mm
@@ -195,6 +195,12 @@ class SortHelper {
   [tableView_ sizeToFit];
 }
 
+- (void)dealloc {
+  [tableView_ setDelegate:nil];
+  [tableView_ setDataSource:nil];
+  [super dealloc];
+}
+
 // Adds a column which has the given string id as title. |isVisible| specifies
 // if the column is initially visible.
 - (NSTableColumn*)addColumnWithId:(int)columnId visible:(BOOL)isVisible {