Null checks to prevent occasional crash

chrome/browser/ui/browser_list.cc

Index: chrome/browser/ui/browser_list.cc
diff --git a/chrome/browser/ui/browser_list.cc b/chrome/browser/ui/browser_list.cc
index 851a9f8ca791e33639009faadca239dc3ef2017c..2c2b64f34594fe8931af99005b8d1c16363750e1 100644
--- a/chrome/browser/ui/browser_list.cc
+++ b/chrome/browser/ui/browser_list.cc
@@ -163,8 +163,10 @@ void BrowserList::TryToCloseBrowserList(const BrowserVector& browsers_to_close,
   on_close_success.Run(profile_path);
 
   for (BrowserVector::const_iterator it = browsers_to_close.begin();
-       it != browsers_to_close.end(); ++it)
-    (*it)->window()->Close();
+       it != browsers_to_close.end(); ++it) {
+    if (*it && (*it)->window())

[Peter Kasting, 2014/10/29 18:07:01]

Can both these be NULL, or just one?

Why do we need checks here but not above?

Is there a precise scenario that causes NULLs that we can describe in a comment
here explaining why the NULL checks are necessary?

[Mike Lerman, 2014/10/29 18:26:06]

I don't know what scenario is causing the NULLs unfortunately - we just have a
crash report, no steps to reproduce. I can't think of what could cause this.
Perhaps contrived javascript, such as an OnBeforeUnload that closes a browser
window, though I don't think you can do that.

The first *it check may not be necessary, but since I don't have steps to
reproduce I'm just playing it safe. My intuition is that the window() is what's
null, though, and can only check (*it)->window() if you prefer.

+      (*it)->window()->Close();
+  }
 }
 
 // static