Reduces the cost of Diff Reflow

Improves the speed of diff (particularly when scrolling in a large diff)
by removing the hover state for line numbers and by removing the pseudo
elements used in visible tabs.

Change-Id: I3c8687ec282696842b51f8f43b76aa267a1506b1

polygerrit-ui/app/elements/diff/gr-diff/gr-diff.html

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 69bd5e4..fda9e35 100644
--- a/polygerrit-ui/app/elements/diff/gr-diff/gr-diff.html
+++ b/polygerrit-ui/app/elements/diff/gr-diff/gr-diff.html
@@ -96,9 +96,6 @@
       .canComment .lineNum[data-value] {
         cursor: pointer;
       }
-      .canComment .lineNum[data-value]:hover:before {
-        background-color: #ccc;
-      }
       .canComment .lineNum[data-value="FILE"]:before {
         content: 'File';
       }
@@ -142,11 +139,9 @@
       .tab {
         display: inline-block;
       }
-      .tab.withIndicator:before {
-        color: #C62828;
-        /* >> character */
-        content: '\00BB';
-        position: absolute;
+      .tab.withIndicator {
+        color: #D68E47;
+        text-decoration: line-through;
       }
     </style>
     <style include="gr-theme-default"></style>