Omnibox Metrics - Add Missing Enum to histograms.xml

These were added to the code in
https://codereview.chromium.org/1855423003

BUG=

Review-Url: https://codereview.chromium.org/2544883004
Cr-Commit-Position: refs/heads/master@{#436126}

tools/metrics/histograms/histograms.xml

@@ -96017,6 +96017,8 @@ value.
   <int value="0" label="via tab"/>
   <int value="1" label="via space at end"/>
   <int value="2" label="via space in middle"/>
+  <int value="3" label="keyboard shortcut"/>
+  <int value="4" label="question mark"/>
 </enum>
 
 <enum name="OmniboxInputType" type="int">