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

components/browser_context_keyed_service/browser_context_dependency_manager.h

Index: components/browser_context_keyed_service/browser_context_dependency_manager.h
diff --git a/components/browser_context_keyed_service/browser_context_dependency_manager.h b/components/browser_context_keyed_service/browser_context_dependency_manager.h
index 6b2ba2620c5c8de943dac6502c4541666f1f2a3e..d51b5d8f081180d45c87924ed9b683ef9fe63888 100644
--- a/components/browser_context_keyed_service/browser_context_dependency_manager.h
+++ b/components/browser_context_keyed_service/browser_context_dependency_manager.h
@@ -68,6 +68,13 @@ class BROWSER_CONTEXT_KEYED_SERVICE_EXPORT BrowserContextDependencyManager {
   // mode. This will NOTREACHED() whenever the user is trying to access a stale
   // BrowserContext*.
   void AssertBrowserContextWasntDestroyed(content::BrowserContext* context);
+
+  // Marks |context| as live (i.e., not stale). This method can be called as a
+  // safeguard against |AssertBrowserContextWasntDestroyed()| checks going off
+  // due to |context| aliasing a BrowserContext instance from a prior test
+  // (i.e., 0xWhatever might be created, be destroyed, and then a new
+  // BrowserContext object might be created at 0xWhatever).
+  void MarkBrowserContextLiveForTesting(content::BrowserContext* context);
 #endif
 
   static BrowserContextDependencyManager* GetInstance();