Make GrDiffGroupRange use LineRange

This is to avoid having two very similar but inconsistent range types in
the API.

Change-Id: I14497e6e2cc0d1c519346bf024894dcf9be6eeed
diff --git a/polygerrit-ui/app/elements/diff/gr-diff-processor/gr-diff-processor.ts b/polygerrit-ui/app/elements/diff/gr-diff-processor/gr-diff-processor.ts
index 5a432dd..a0584b6 100644
--- a/polygerrit-ui/app/elements/diff/gr-diff-processor/gr-diff-processor.ts
+++ b/polygerrit-ui/app/elements/diff/gr-diff-processor/gr-diff-processor.ts
@@ -371,8 +371,11 @@
     group.ignoredWhitespaceOnly = !!chunk.common;
     if (chunk.skip) {
       group.lineRange = {
-        left: {start: offsetLeft, end: offsetLeft + chunk.skip - 1},
-        right: {start: offsetRight, end: offsetRight + chunk.skip - 1},
+        left: {start_line: offsetLeft, end_line: offsetLeft + chunk.skip - 1},
+        right: {
+          start_line: offsetRight,
+          end_line: offsetRight + chunk.skip - 1,
+        },
       };
     }
     return group;