Fixed crash if tab closes while WebShare picker dialog is open.

chrome/browser/webshare/share_service_impl.h

Index: chrome/browser/webshare/share_service_impl.h
diff --git a/chrome/browser/webshare/share_service_impl.h b/chrome/browser/webshare/share_service_impl.h
index ed1cde8113f86719a26aefc1cd29e1dd36056790..7fb1609314efcded6284bc0b1d9b5da524fb58b2 100644
--- a/chrome/browser/webshare/share_service_impl.h
+++ b/chrome/browser/webshare/share_service_impl.h
@@ -10,6 +10,7 @@
 #include <vector>
 
 #include "base/gtest_prod_util.h"
+#include "base/memory/weak_ptr.h"
 #include "base/strings/string16.h"
 #include "chrome/browser/ui/browser.h"
 #include "chrome/browser/ui/browser_dialogs.h"
@@ -89,6 +90,8 @@ class ShareServiceImpl : public blink::mojom::ShareService {
                       const ShareCallback& callback,
                       base::Optional<std::string> result);
 
+  base::WeakPtrFactory<ShareServiceImpl> weak_factory_;
+
   DISALLOW_COPY_AND_ASSIGN(ShareServiceImpl);
 };