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..bffd9270a680ec30bc19a070673defffec780b00 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 +68,11 @@ 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);
+
+  // Indicates that |context| is live (i.e., not stale). Called as a safeguard
+  // against |AssertBrowserContextWasntDestroyed()| checks going off due to
+  // |context| aliasing a BrowserContext instance from a prior test.
+  void MarkBrowserContextLiveForTesting(content::BrowserContext* context);
 #endif
 
   static BrowserContextDependencyManager* GetInstance();