Addition of the UserDataFolder API for review

Author: David Shoemaker

specs/UserDataFolder.md

@@ -0,0 +1,98 @@
+
+Title
+===
+UserDataFolder API 
+
+# Background
+You may have a need to cleanup or possibly add to the data being
+stored in the WebView2 user data directory.  This directory can be either 
+configured by the you during creation of the webview2 control or calculated
+at runtime by the control if it wasn't set during creation.
+
+The current WebView2 code is designed to use a the directory that the hosting 
+application is running in as the default location.  This has resulted in issues 
+if running from a secure location (IE the program files tree).  Work is in process
+to change that default and will be forthcoming in later changes
+
+With the current guidance it is possible for you to have built
+logic into your application with an assumption where the User Data is 
+located.  WebView2 changing that default can then result in a code error or 
+possible crash.
+
+This api will provide the you a way to get the directory that is 
+currently being used by the WebView for storage of the user data.
+
+Using this returned directory is safer for the long run so that if WebView2 
+changes the underlying path default logic the application will be able to adapt 
+automatically.
+
+
+# Description
+
+Returns the user data folder that all CoreWebView2's created from this 
+environment are using.
+This could be either the value passed in by you when creating the 
+environment object or the calculated one for default handling.  And it will
+always be an absolute path.
+
+
+# Examples
+
+```cpp
+HRESULT UserDataFolder()
+{
+  base::ScopedTempDir temp_dir;
+
+  CreateCoreWebView2EnvironmentWithOptions(
+      L".", temp_dir.GetPath().value().c_str(), nullptr,
+    Microsoft::WRL::Callback<
+      ICoreWebView2CreateCoreWebView2EnvironmentCompletedHandler>
+    (
+          [&temp_dir, &environment_created]
+        (HRESULT result, ICoreWebView2Environment* webview_environment) ->
+            HRESULT {
+
+            ScopedCoMemString environmentUserDataFolder;
+            webview_environment->get_UserDataFolder(
+                &environmentUserDataFolder);
+
+            return S_OK;
+    }).Get());
+
+    return S_OK;_
+}
+```
+
+```c#
+
+    /// Webview creation and setup of completion handler are out of scope of sample
+    void WebView_CoreWebView2InitializationCompleted(object sender, CoreWebView2InitializationCompletedEventArgs e)
+    {
+        if (e.IsSuccess)
+        {
+            String userDataFolder = webView.CoreWebView2.Environment->UserDataFolder();
+        }
+    }
+
+```
+
+# API Details
+```c# (but really MIDL3)
+/// This interface is an extension of the ICoreWebView2Environment. An object
+/// implementing the ICoreWebView2Environment5 interface will also
+/// implement ICoreWebView2Environment.
+[
+  uuid(083CB0D7-E464-4108-807E-80AE4EAA3B28), object,
+  pointer_default(unique)
+] interface ICoreWebView2Environment6 : IUnknown {
+  /// Returns the user data folder that all CoreWebView2's created from this 
+  /// environment are using.
+  /// This could be either the value passed in by the developer when creating the 
+  /// environment object or the calculated one for default handling.  And will
+  /// always be an absolute path.
+  ///
+  /// \snippet AppWindow.cpp GetUserDataFolder
+
+  [propget] HRESULT UserDataFolder([ out, retval ] LPWSTR * value);
+}
+```