Add chromecast/internal to the visibility list of libxml.

Bug: internal b/144557463
Bug: 1101110
Test: Build
Change-Id: I39549934fb7234b58c664337acd05232d60d0875
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2265434
Commit-Queue: Junbo Ke <juke@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#784224}

third_party/libxml/BUILD.gn

@@ -137,6 +137,7 @@ static_library("libxml") {
     ":xml_reader",
     ":xml_writer",
     ":libxml_utils",
+    "//chromecast/internal",
     "//testing/libfuzzer/*",
     "//third_party/blink/renderer/*",
     "//third_party/fontconfig",