Add Spec: Critical Restart Required (#4657)

* Add Spec: Critical Kill Switch (#4574)

* add critical api

---------

Co-authored-by: Diana Qu <xiaqu@microsoft.com>
Co-authored-by: David Risney <dave@deletethis.net>

* Sample code update

Co-authored-by: MikeHillberg <18429489+MikeHillberg@users.noreply.github.com>

* Fix typo

Co-authored-by: Viktoria Zlatinova <vizlatin@microsoft.com>

* renaming API and update doc

* renaming md file

---------

Co-authored-by: Diana Qu <xiaqu@microsoft.com>
Co-authored-by: David Risney <dave@deletethis.net>
Co-authored-by: MikeHillberg <18429489+MikeHillberg@users.noreply.github.com>
Co-authored-by: Viktoria Zlatinova <vizlatin@microsoft.com>

Author: 5 people

specs/RestartRequested.md

@@ -0,0 +1,107 @@
+Critical Update Available
+===
+
+# Background
+As WebView2 developers, we often have to author ECS (experimentation and configuration service - 
+used to perform A/B testing or remotely disable features) configurations to toggle feature flags. 
+However, once these payloads are received, there is no way to restart the WebView2 and apply the
+payload. The purpose of this API is to detect such critical payloads and inform the end developer
+so they may restart their app or their WebView2 or other appropriate action.
+
+# Examples
+## WinRT and .NET   
+```c#
+void WebView_CoreWebView2InitializationCompleted(object sender, CoreWebView2InitializationCompletedEventArgs e)
+{
+    if (e.IsSuccess)
+    {
+        // ...
+        webView.CoreWebView2.Environment.RestartRequested += WebView_RestartRequested;
+    }
+}
+
+void WebView_RestartRequested(CoreWebView2Environment sender, object e)
+{
+    // Depending on your app experience, you may or may not
+    // want to prompt user to restart the app.
+    RestartIfSelectedByUser();
+}
+```
+
+## Win32 C++
+```cpp
+wil::com_ptr<ICoreWebView2Environment> m_webViewEnvironment;
+void CoreWebView2InitializationCompleted() {
+    auto env10 = m_webViewEnvironment.try_query<ICoreWebView2Environment10>();
+    if (env10) {
+        CHECK_FAILURE(env10->add_RestartRequested(
+            Callback<ICoreWebView2RestartRequestedEventHandler>(
+                [this](ICoreWebView2Environment* sender, IUnknown* args) -> HRESULT
+                {
+                    // Depending on your app experience, you may or may not
+                    // want to prompt user to restart the app.
+                    RestartIfSelectedByUser();
+                    return S_OK;
+                })
+                .Get(),
+            nullptr));
+    }
+}
+```
+
+# API Notes
+
+See [API Details](#api-details) section below for API reference.
+
+# API Details
+## Win32 C++
+
+```IDL
+interface ICoreWebView2Environment10;
+interface ICoreWebView2RestartRequestedEventHandler;
+
+[uuid(62cb67c6-b6a9-4209-8a12-72ca093b9547), object, pointer_default(unique)]
+interface ICoreWebView2RestartRequestedEventHandler : IUnknown {
+  /// Provides the event args for the corresponding event.  No event args exist
+  /// and the `args` parameter is set to `null`.
+  HRESULT Invoke([in] ICoreWebView2Environment* sender, [in] IUnknown* args);
+}
+
+[uuid(ef7632ec-d86e-46dd-9d59-e6ffb5c87878), object, pointer_default(unique)]
+interface ICoreWebView2Environment10 : IUnknown {
+  /// Add an event handler for the `RestartRequested` event.
+  /// `RestartRequested` event is raised when there is an urgent need to 
+  /// restart the WebView2 process in order to enable or disable 
+  /// features that are causing WebView2 reliability or performance to drop critically.
+  /// `RestartRequested` gives you the awareness of these necessary WebView2 restarts,
+  /// allowing you to resolve issues faster than waiting for your end users to restart the app.
+  /// Depending on your app you may want to prompt your end users in some way to give
+  /// them a chance to save their state before you restart the WebView2.
+  /// 
+  /// For apps with multiple processes that host WebView2s that share the same user data folder you
+  /// need to make sure all WebView2 instances are closed and the associated WebView2 Runtime
+  /// browser process exits. See `BrowserProcessExited` for more details.
+  // MSOWNERS: xiaqu@microsoft.com
+  HRESULT add_RestartRequested(
+      [in] ICoreWebView2RestartRequestedEventHandler* eventHandler,
+      [out] EventRegistrationToken* token);
+
+  /// Remove an event handler previously added with `add_RestartRequested`.
+  // MSOWNERS: xiaqu@microsoft.com
+  HRESULT remove_RestartRequested(
+      [in] EventRegistrationToken token);
+}
+```
+s
+## .NET and WinRT
+
+```c#
+namespace Microsoft.Web.WebView2.Core
+{
+    runtimeclass CoreWebView2Environment
+    {
+        // ...
+        event Windows.Foundation.TypedEventHandler<CoreWebView2Environment, Object> RestartRequested;
+    }
+}
+```