Show blame in diff

With this change a blame column is added to the left side of diff
tables. The column is empty and hidden until blame is loaded. A button
is added to the change view to trigger a load of the blame for that
diff, as well as a unload it if already loaded. In this stage, the blame
information is non-interactive and only displays the SHA, date and
commit author.

Feature: Issue 6075
Change-Id: Ifcb951265d0e6339094e6b7c9574ec9c69e60b51
diff --git a/polygerrit-ui/app/elements/diff/gr-diff/gr-diff.html b/polygerrit-ui/app/elements/diff/gr-diff/gr-diff.html
index 7ef5c60..7b84ef5 100644
--- a/polygerrit-ui/app/elements/diff/gr-diff/gr-diff.html
+++ b/polygerrit-ui/app/elements/diff/gr-diff/gr-diff.html
@@ -212,6 +212,32 @@
       #sizeWarning.warn {
         display: block;
       }
+      .target-row td.blame {
+        background: #eee;
+      }
+      td.blame {
+        display: none;
+        font-family: var(--font-family);
+        font-size: var(--font-size, 12px);
+        padding: 0 .5em;
+        white-space: pre;
+      }
+      :host(.showBlame) td.blame {
+        display: table-cell;
+      }
+      td.blame > span {
+        opacity: 0.6;
+      }
+      td.blame > span.startOfRange {
+        opacity: 1;
+      }
+      td.blame .sha {
+        font-family: var(--monospace-font-family);
+      }
+      .full-width td.blame {
+        overflow: hidden;
+        width: 200px;
+      }
     </style>
     <style include="gr-theme-default"></style>
     <div id="diffHeader" hidden$="[[_computeDiffHeaderHidden(_diffHeaderItems)]]">