Add tests for showing join screen

Adds fake UI delegate, and reuse the existing fake SDK delegate.
Utility to override the delegates in the factory that creates them.
Ability to override the preview data in native service, and fake proxy
server for this reason.

Bug: 406947978
Change-Id: I7743f68b5ef5aee6b3daeb0084775ef59564d052
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6448081
Reviewed-by: Hailey Wang <[email protected]>
Commit-Queue: Siddhartha S <[email protected]>
Cr-Commit-Position: refs/heads/main@{#1446107}
diff --git a/chrome/browser/data_sharing/BUILD.gn b/chrome/browser/data_sharing/BUILD.gn
index a114f87..026474d58 100644
--- a/chrome/browser/data_sharing/BUILD.gn
+++ b/chrome/browser/data_sharing/BUILD.gn
@@ -209,6 +209,7 @@
     resources_package = "org.chromium.chrome.browser.data_sharing"
     sources = [
       "android/java/src/org/chromium/chrome/browser/data_sharing/DataSharingImplFactory.java",
+      "android/java/src/org/chromium/chrome/browser/data_sharing/FakeDataSharingUIDelegateImpl.java",
       "android/java/src/org/chromium/chrome/browser/data_sharing/NoOpDataSharingSDKDelegateImpl.java",
     ]