Add privileged access to ClipboardHistory

EndpointType::kClipboardHistory was added
in crrev.com/c/2362289, so that ClipboardHistory
will have access to any clipboard data, but
the logic of EnterpriseClipboardDlpController::
IsReadAllowed didn't include kClipboardHistory
when it got implemented.

Bug: 1139835
Change-Id: I5f7fcd9e05a2a2f424b7ff1932edec557d23180f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2487288Reviewed-by: Nikita Podguzov <nikitapodguzov@chromium.org>
Commit-Queue: Aya Elsayed <ayaelattar@chromium.org>
Cr-Commit-Position: refs/heads/master@{#819326}

chrome/browser/chromeos/policy/dlp/enterprise_clipboard_dlp_controller.cc

@@ -41,7 +41,7 @@ void EnterpriseClipboardDlpController::Init() {
 bool EnterpriseClipboardDlpController::IsDataReadAllowed(
     const ui::ClipboardDataEndpoint* const data_src,
     const ui::ClipboardDataEndpoint* const data_dst) const {
-  if (!data_src) {
+  if (!data_src || data_src->type() == ui::EndpointType::kClipboardHistory) {
     return true;
   }