[omnibox]: Classify document suggestion descriptions as DIM

Currently, search suggestions' descriptions (e.g. the 'Google Search'
suffix) are classified DIM. However, document suggestions' descriptions
(e.g. the 'Apr 3 - Google Docs' suffix) are classified NONE.

Bug: 366623
Change-Id: I14ea6d9e9342e5793cfa73762e0efc233fe3df23
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1555353Reviewed-by: Justin Donnelly <jdonnelly@chromium.org>
Commit-Queue: manuk hovanesian <manukh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#649894}

components/omnibox/browser/document_provider.cc

@@ -514,7 +514,7 @@ bool DocumentProvider::ParseDocumentSearchResults(const base::Value& root_val,
         match.description = GetProductDescriptionString(mimetype);
       }
       AutocompleteMatch::AddLastClassificationIfNecessary(
-          &match.description_class, 0, ACMatchClassification::NONE);
+          &match.description_class, 0, ACMatchClassification::DIM);
     }
     match.transition = ui::PAGE_TRANSITION_GENERATED;
     if (!in_counterfactual_group) {