Diffs in PolyGerrit apply two shades of highlight to changed lines
(light and dark) to indicate the granularity of modifications and to
distinguish intraline edits. However, the logic for choosing the
background shade for diff lines would differ from that of GWT UI diffs
subtly.
+----------------------------------+----------------------------------+
| GWT UI Shading Logic | PG Shading Logic (incorrect) |
+----------------------------------+----------------------------------+
| Diff lines get a dark background | Diff lines get a dark background |
| IFF they appear in a delta chunk | IFF they do NOT contain any |
| that is empty on the left OR | intraline differences. |
| empty on the right. | |
+----------------------------------+----------------------------------+
| Diff lines get a light background otherwise. |
+---------------------------------------------------------------------+
With this change, the shading logic in PolyGerrit is modified to match
that of the GWT UI.
Bug: Issue 4219
Bug: Issue 5117
Change-Id: Ice24292df777118c08c3e73f771720f8a186a183
1e3cd47707