[omnibox] Fix a bug with OmniboxPopupModel::TriggerSelectionAction

OmniboxPopupModel::TriggerSelectionAction will definitely crash in the
no-default-match edge case, which can definitely happen with certain
enterprise policies.

Additionally, it's possible that UI callers will pass in an invalid
|selection|, as they are an external class that could potentially be
stale. In practice, it doesn't SEEM possible for this to occur with
Views, but I'm not sure.

Philosophically, I think crashing when the UI code gets out of date
isn't a good thing, and this code should be a bit more tolerant.

Bug: 1085407, 1078183, 1052522
Change-Id: Ibe5a2b09340679d3bfb86c234bc799f0823fdaaf
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2216605Reviewed-by: Justin Donnelly <jdonnelly@chromium.org>
Commit-Queue: Tommy Li <tommycli@chromium.org>
Cr-Commit-Position: refs/heads/master@{#772420}

components/omnibox/browser/omnibox_popup_model.cc

@@ -563,9 +563,14 @@ void OmniboxPopupModel::SetSelection(Selection selection) {
 }
 
 bool OmniboxPopupModel::TriggerSelectionAction(Selection selection) {
+  // Early exit for the kNoMatch case. Also exits if the calling UI passes in
+  // an invalid |selection|.
+  if (selection.line >= result().size())
+    return false;
+
   auto& match = result().match_at(selection.line);
-  if (selection.state == HEADER_BUTTON_FOCUSED) {
-    DCHECK(match.suggestion_group_id.has_value());
+  if (selection.state == HEADER_BUTTON_FOCUSED &&
+      match.suggestion_group_id.has_value()) {
     omnibox::ToggleSuggestionGroupIdVisibility(
         pref_service_, match.suggestion_group_id.value());
     return true;