Make web store resilient against download completion happening before opening.

content/public/test/download_test_observer.h

Index: content/public/test/download_test_observer.h
diff --git a/content/public/test/download_test_observer.h b/content/public/test/download_test_observer.h
index 8df29882e721d00190c21ea4411ac1582457f614..02299cc476d5866ebcc458ad966976ba3d5fa305 100644
--- a/content/public/test/download_test_observer.h
+++ b/content/public/test/download_test_observer.h
@@ -9,6 +9,7 @@
 #include <vector>
 
 #include "base/basictypes.h"
+#include "base/callback_forward.h"
 #include "base/memory/ref_counted.h"
 #include "content/public/browser/download_item.h"
 #include "content/public/browser/download_manager.h"
@@ -17,6 +18,36 @@
 
 namespace content {
 
+// Detects an arbitrary change on a download item.
+// TODO: Rewrite other observers to use this (or be replaced by it).
+class DownloadUpdatedObserver : public DownloadItem::Observer {
+ public:
+  typedef base::Callback<bool(DownloadItem*)> EventFilter;
+
+  // The filter passed may be called multiple times, even after it
+  // returns true.
+  DownloadUpdatedObserver(DownloadItem* item, EventFilter filter);
+  virtual ~DownloadUpdatedObserver();
+
+  // Returns when either the event has been seen (at least once since
+  // object construction) or the item is destroyed.  Return value indicates
+  // if the wait ended because the item was seen (true) or the object
+  // destroyed (false).
+  bool WaitForEvent();
+
+ private:
+  // DownloadItem::Observer
+  virtual void OnDownloadUpdated(DownloadItem* item) OVERRIDE;
+  virtual void OnDownloadDestroyed(DownloadItem* item) OVERRIDE;
+
+  DownloadItem* item_;
+  EventFilter filter_;
+  bool waiting_;
+  bool event_seen_;
+
+  DISALLOW_COPY_AND_ASSIGN(DownloadUpdatedObserver);
+};
+
 // Detects changes to the downloads after construction.
 // Finishes when one of the following happens:
 //   - A specified number of downloads change to a terminal state (defined