[Chromium] Show private mode about page

When entering private mode Wolvic displays a custom web page
that explains the user what private mode is and what is not.

In the case of Chromium backend it was not showing anything
because the Session::loadData interface was not implemented.
This PR implements it using the new API added in
Igalia/wolvic-chromium#119

app/src/common/chromium/com/igalia/wolvic/browser/api/impl/SessionImpl.java

@@ -1,6 +1,7 @@
 package com.igalia.wolvic.browser.api.impl;
 
 import android.graphics.Matrix;
+import android.util.Base64;
 import android.view.ViewGroup;
 
 import androidx.annotation.AnyThread;
@@ -92,8 +93,9 @@ public void loadUri(@NonNull String uri, int flags) {
     }
 
     @Override
-    public void loadData(@NonNull byte[] data, String mymeType) {
-        // TODO: Implement
+    public void loadData(@NonNull byte[] data, String mimeType) {
+        if (isOpen())
+            mTab.loadData(Base64.encodeToString(data, Base64.NO_WRAP), mimeType, "base64");
     }
 
     @Override