Eliminate potential for flaky crash in BCKSFactory::SetTestingFactory().

components/browser_context_keyed_service/browser_context_dependency_manager.cc

Index: components/browser_context_keyed_service/browser_context_dependency_manager.cc
diff --git a/components/browser_context_keyed_service/browser_context_dependency_manager.cc b/components/browser_context_keyed_service/browser_context_dependency_manager.cc
index 913c92b80858a7f4489bb486e84cf0ab874dfdef..bd45e7a8cd5837baddabd236db0edcae0524faeb 100644
--- a/components/browser_context_keyed_service/browser_context_dependency_manager.cc
+++ b/components/browser_context_keyed_service/browser_context_dependency_manager.cc
@@ -71,11 +71,7 @@ void BrowserContextDependencyManager::DoCreateBrowserContextServices(
   TRACE_EVENT0("browser",
     "BrowserContextDependencyManager::DoCreateBrowserContextServices")
 #ifndef NDEBUG
-  // Unmark |context| as dead. This exists because of unit tests, which will
-  // often have similar stack structures. 0xWhatever might be created, go out
-  // of scope, and then a new BrowserContext object might be created
-  // at 0xWhatever.
-  dead_context_pointers_.erase(context);
+  MarkBrowserContextLiveForTesting(context);
 #endif
 
   std::vector<DependencyNode*> construction_order;
@@ -139,6 +135,11 @@ void BrowserContextDependencyManager::AssertBrowserContextWasntDestroyed(
                  << "services again.";
   }
 }
+
+void BrowserContextDependencyManager::MarkBrowserContextLiveForTesting(
+    content::BrowserContext* context) {
+  dead_context_pointers_.erase(context);
+}
 #endif
 
 // static