Unify ranges to use snake_case

For consistency with the API [1], to make it less confusing.

[1] https://gerrit-review.googlesource.com/Documentation/rest-api-changes.html#comment-range

Change-Id: I1a77af83bdeadfce4baa629a500a6ea04762e856
diff --git a/polygerrit-ui/app/elements/diff/gr-diff-host/gr-diff-host_test.html b/polygerrit-ui/app/elements/diff/gr-diff-host/gr-diff-host_test.html
index c7ee1c2..423bdc6 100644
--- a/polygerrit-ui/app/elements/diff/gr-diff-host/gr-diff-host_test.html
+++ b/polygerrit-ui/app/elements/diff/gr-diff-host/gr-diff-host_test.html
@@ -966,10 +966,10 @@
 
       // Try to fetch a thread with a different range.
       range = {
-        startLine: 1,
-        startChar: 1,
-        endLine: 1,
-        endChar: 3,
+        start_line: 1,
+        start_character: 1,
+        end_line: 1,
+        end_character: 3,
       };
 
       assert.isOk(element._getOrCreateThread(