Add SetTestingFactoryAndUse variant for KeyedService subclasses

SetTestingFactoryAndUse often requires users to do two casts
themselves: an upcast of their service to KeyedService in their
TestingFactory implementation, then a downcast from KeyedService to
their service subclass on the result.

This adds a method, SetTestingSubclassFactoryAndUse, which does these
casts internally.

Change-Id: I6d77d06dd06ebcb212498e2692f2ec9f1fb584b0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2244095
Commit-Queue: Collin Baker <collinbaker@chromium.org>
Reviewed-by: Henrique Nakashima <hnakashima@chromium.org>
Cr-Commit-Position: refs/heads/master@{#779614}

chrome/browser/ui/views/tabs/tab_groups_iph_controller_unittest.cc

@@ -25,7 +25,13 @@ class TabGroupsIPHControllerTest : public BrowserWithTestWindowTest {
  public:
   void SetUp() override {
     BrowserWithTestWindowTest::SetUp();
-    mock_tracker_ = InjectTrackerForProfile(GetProfile());
+    mock_tracker_ =
+        feature_engagement::TrackerFactory::GetInstance()
+            ->SetTestingSubclassFactoryAndUse(
+                GetProfile(), base::BindRepeating([](content::BrowserContext*) {
+                  return std::make_unique<
+                      feature_engagement::test::MockTracker>();
+                }));
 
     // Other features call into the IPH backend. We don't want to fail
     // on their calls, so allow them. Our test cases will set
@@ -38,19 +44,6 @@ class TabGroupsIPHControllerTest : public BrowserWithTestWindowTest {
 
  protected:
   feature_engagement::test::MockTracker* mock_tracker_;
-
- private:
-  static feature_engagement::test::MockTracker* InjectTrackerForProfile(
-      Profile* profile) {
-    KeyedService* const tracker =
-        feature_engagement::TrackerFactory::GetInstance()
-            ->SetTestingFactoryAndUse(profile, base::Bind(MakeTracker));
-    return static_cast<feature_engagement::test::MockTracker*>(tracker);
-  }
-
-  static std::unique_ptr<KeyedService> MakeTracker(content::BrowserContext*) {
-    return std::make_unique<feature_engagement::test::MockTracker>();
-  }
 };
 
 TEST_F(TabGroupsIPHControllerTest, NotifyEventAndTriggerOnSixthTabOpened) {

components/keyed_service/content/browser_context_keyed_service_factory.h

@@ -7,6 +7,8 @@
 
 #include <memory>
 
+#include "base/bind.h"
+#include "base/callback.h"
 #include "base/compiler_specific.h"
 #include "base/macros.h"
 #include "components/keyed_service/core/keyed_service_export.h"
@@ -48,6 +50,34 @@ class KEYED_SERVICE_EXPORT BrowserContextKeyedServiceFactory
   KeyedService* SetTestingFactoryAndUse(content::BrowserContext* context,
                                         TestingFactory testing_factory);
 
+  // A variant of |TestingFactory| for supplying a subclass of
+  // KeyedService for a given BrowserContext.
+  template <typename Derived>
+  using TestingSubclassFactory =
+      base::RepeatingCallback<std::unique_ptr<Derived>(
+          content::BrowserContext* context)>;
+
+  // Like |SetTestingFactoryAndUse|, but instead takes a factory for a
+  // subclass of KeyedService and returns a pointer to this subclass.
+  // This allows callers to avoid using static_cast in both directions:
+  // casting up to KeyedService in their factory, and casting down to
+  // their subclass on the returned pointer.
+  template <typename Derived>
+  Derived* SetTestingSubclassFactoryAndUse(
+      content::BrowserContext* context,
+      TestingSubclassFactory<Derived> derived_factory) {
+    TestingFactory upcast_factory = base::BindRepeating(
+        [](TestingSubclassFactory<Derived> derived_factory,
+           content::BrowserContext* context) {
+          return std::unique_ptr<KeyedService>(
+              derived_factory.Run(context).release());
+        },
+        std::move(derived_factory));
+
+    return static_cast<Derived*>(
+        SetTestingFactoryAndUse(context, std::move(upcast_factory)));
+  }
+
  protected:
   // BrowserContextKeyedServiceFactories must communicate with a
   // BrowserContextDependencyManager. For all non-test code, write your subclass