fix: InAppPurchase pre-emptive deallocation (#40938)

* fix: InAppPurchase pre-emptive deallocation

* test: try re-enabling IAP tests

shell/browser/mac/in_app_purchase.mm

@@ -26,6 +26,7 @@
   in_app_purchase::InAppPurchaseCallback callback_;
   NSInteger quantity_;
   NSString* username_;
+  InAppPurchase __strong* self_;
 }
 
 - (id)initWithCallback:(in_app_purchase::InAppPurchaseCallback)callback
@@ -53,6 +54,7 @@
     callback_ = std::move(callback);
     quantity_ = quantity;
     username_ = [username copy];
+    self_ = self;
   }
 
   return self;
@@ -91,6 +93,7 @@
   // Return if the product is not found or invalid.
   if (product == nil) {
     [self runCallback:false];
+    self_ = nil;
     return;
   }
 
@@ -114,6 +117,7 @@
 
   // Notify that the payment has been added to the queue with success.
   [self runCallback:true];
+  self_ = nil;
 }
 
 /**
@@ -128,10 +132,6 @@
   }
 }
 
-- (void)dealloc {
-  username_ = nil;
-}
-
 @end
 
 // ============================================================================

shell/browser/mac/in_app_purchase_product.mm

@@ -24,6 +24,7 @@
 @interface InAppPurchaseProduct : NSObject <SKProductsRequestDelegate> {
  @private
   in_app_purchase::InAppPurchaseProductsCallback callback_;
+  InAppPurchaseProduct __strong* self_;
 }
 
 - (id)initWithCallback:(in_app_purchase::InAppPurchaseProductsCallback)callback;
@@ -43,6 +44,7 @@
     (in_app_purchase::InAppPurchaseProductsCallback)callback {
   if ((self = [super init])) {
     callback_ = std::move(callback);
+    self_ = self;
   }
 
   return self;
@@ -81,6 +83,7 @@
   // Send the callback to the browser thread.
   content::GetUIThreadTaskRunner({})->PostTask(
       FROM_HERE, base::BindOnce(std::move(callback_), converted));
+  self_ = nil;
 }
 
 /**