[DevUI DFM] Improve DevUiModuleProvider testability.

Previously, class DevUiModuleProvider consists of static functions
{ModuleInstalled(), InstallModule(), LoadModule} that are called
directly. Unfortunately, these cannot be mocked for testing.

This CL makes DevUiModuleProvider a singleton class that's accessed
via GetInstance(). SetTestInstance() is added to allow a test to
override DevUiModuleProvider functions, and inject a test instance
that replaces the original singleton obtained from GetInstance().

Bug: 927131
TBR: yfriedman@chromium.org
Change-Id: Ifee6899ebf67be17ad2ed15103b9c7b6d8e322a2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1863553Reviewed-by: Samuel Huang <huangs@chromium.org>
Reviewed-by: Tibor Goldschwendt <tiborg@chromium.org>
Reviewed-by: Andrew Grieve <agrieve@chromium.org>
Commit-Queue: Samuel Huang <huangs@chromium.org>
Cr-Commit-Position: refs/heads/master@{#706160}

chrome/android/modules/dev_ui/provider/dev_ui_module_provider.cc

@@ -13,12 +13,30 @@
 namespace dev_ui {
 
 // static
+DevUiModuleProvider* DevUiModuleProvider::test_instance_ = nullptr;
+
+// Destructor is public to enable management by std::unique_ptr<>.
+DevUiModuleProvider::~DevUiModuleProvider() = default;
+
+// static
+DevUiModuleProvider* DevUiModuleProvider::GetInstance() {
+  if (test_instance_)
+    return test_instance_;
+
+  static DevUiModuleProvider instance;
+  return &instance;
+}
+
+// static
+void DevUiModuleProvider::SetTestInstance(DevUiModuleProvider* test_instance) {
+  test_instance_ = test_instance;
+}
+
 bool DevUiModuleProvider::ModuleInstalled() {
   return Java_DevUiModuleProvider_isModuleInstalled(
       base::android::AttachCurrentThread());
 }
 
-// static
 void DevUiModuleProvider::InstallModule(
     base::OnceCallback<void(bool)> on_complete) {
   auto* listener = DevUiInstallListener::Create(std::move(on_complete));
@@ -28,13 +46,10 @@ void DevUiModuleProvider::InstallModule(
                                          listener->j_listener());
 }
 
-// static
 void DevUiModuleProvider::LoadModule() {
   Java_DevUiModuleProvider_loadModule(base::android::AttachCurrentThread());
 }
 
 DevUiModuleProvider::DevUiModuleProvider() = default;
 
-DevUiModuleProvider::~DevUiModuleProvider() = default;
-
 }  // namespace dev_ui

chrome/android/modules/dev_ui/provider/dev_ui_module_provider.h

@@ -11,23 +11,33 @@ namespace dev_ui {
 
 class DevUiModuleProvider {
  public:
+  // Returns the singleton, which can be overridden using SetTestInstance().
+  static DevUiModuleProvider* GetInstance();
+
+  // Overrides the singleton with caller-owned |test_instance|. Caller tests
+  // are responsible for resetting this to null on cleanup.
+  static void SetTestInstance(DevUiModuleProvider* test_instance);
+
   // Returns true if the DevUI module is installed.
-  static bool ModuleInstalled();
+  virtual bool ModuleInstalled();
 
   // Asynchronously requests to install the DevUI module. |on_complete| is
   // called after the module install is completed, and takes a bool to indicate
   // whether module install is successful.
-  static void InstallModule(base::OnceCallback<void(bool)> on_complete);
+  virtual void InstallModule(base::OnceCallback<void(bool)> on_complete);
 
   // Assuming that the DevUI module is installed, loads DevUI resources if not
   // already loaded.
-  static void LoadModule();
+  virtual void LoadModule();
 
- private:
+ protected:
   DevUiModuleProvider();
-  ~DevUiModuleProvider();
+  virtual ~DevUiModuleProvider();
   DevUiModuleProvider(const DevUiModuleProvider&) = delete;
   DevUiModuleProvider& operator=(const DevUiModuleProvider&) = delete;
+
+ private:
+  static DevUiModuleProvider* test_instance_;
 };
 
 }  // namespace dev_ui

chrome/browser/android/dev_ui/dev_ui_url_handler.cc

@@ -83,9 +83,9 @@ bool HandleDfmifiedDevUiPageURL(
   }
 
   // If module is already installed, ensure that it is loaded.
-  if (dev_ui::DevUiModuleProvider::ModuleInstalled()) {
+  if (dev_ui::DevUiModuleProvider::GetInstance()->ModuleInstalled()) {
     // Synchronously load module (if not already loaded).
-    dev_ui::DevUiModuleProvider::LoadModule();
+    dev_ui::DevUiModuleProvider::GetInstance()->LoadModule();
     return false;
   }
   // Create URL to the DevUI loader with "?url=<escaped original URL>" so that

chrome/browser/ui/webui/android/dev_ui_loader/dev_ui_loader_message_handler.cc

@@ -28,9 +28,10 @@ void DevUiLoaderMessageHandler::HandleGetDevUiDfmState(
     const base::ListValue* args) {
   const base::Value* callback_id = nullptr;
   CHECK(args->Get(0, &callback_id));
-  const char* response = dev_ui::DevUiModuleProvider::ModuleInstalled()
-                             ? "installed"
-                             : "not-installed";
+  const char* response =
+      dev_ui::DevUiModuleProvider::GetInstance()->ModuleInstalled()
+          ? "installed"
+          : "not-installed";
   AllowJavascript();
   ResolveJavascriptCallback(*callback_id, base::Value(response));
 }
@@ -49,8 +50,8 @@ void DevUiLoaderMessageHandler::HandleInstallDevUiDfm(
   const base::Value* callback_id = nullptr;
   CHECK(args->Get(0, &callback_id));
 
-  if (!dev_ui::DevUiModuleProvider::ModuleInstalled()) {
-    dev_ui::DevUiModuleProvider::InstallModule(base::BindOnce(
+  if (!dev_ui::DevUiModuleProvider::GetInstance()->ModuleInstalled()) {
+    dev_ui::DevUiModuleProvider::GetInstance()->InstallModule(base::BindOnce(
         &DevUiLoaderMessageHandler::OnDevUiDfmInstallWithStatus,
         weak_ptr_factory_.GetWeakPtr(), callback_id->GetString()));
   } else {