Fix InstallStageTracker::NotifyObserversOfFailure

InstallStageTracker::Observer::OnExtensionInstallationFailed may remove
the observers and thus change the object. Immediately after calling
this method, OnExtensionDataChangedForTesting method is called which
might result in a crash. The observers list is traversed again after
calling the method OnExtensionInstallationFailed so that only
the updated observers are used.

Bug: 1097700
Change-Id: I0c0721179d8b737e14748b2d5965926ad6a1bf88
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2257318
Commit-Queue: Swapnil Gupta <swapnilgupta@google.com>
Reviewed-by: Oleg Davydov <burunduk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#781397}

chrome/browser/extensions/forced_extensions/install_stage_tracker.cc

@@ -253,10 +253,12 @@ void InstallStageTracker::NotifyObserversOfFailure(
     const ExtensionId& id,
     FailureReason reason,
     const InstallationData& data) {
-  for (auto& observer : observers_) {
+  for (auto& observer : observers_)
     observer.OnExtensionInstallationFailed(id, reason);
+  // Observer::OnExtensionInstallationFailed may change |observers_|, run the
+  // loop again to call the other methods for |observers_|.
+  for (auto& observer : observers_)
     observer.OnExtensionDataChangedForTesting(id, browser_context_, data);
-  }
 }
 
 }  //  namespace extensions