Clearly mark the new/old diff with a css class

This is super useful for debugging, because the new diff is supposed to
"look" identical to the old diff. :-)

Release-Notes: skip
Change-Id: I243ad8bcfc0848f7c144170a0e7fd49f303d897b
diff --git a/polygerrit-ui/app/embed/diff-old/gr-diff/gr-diff.ts b/polygerrit-ui/app/embed/diff-old/gr-diff/gr-diff.ts
index 2aa8096..0da3522 100644
--- a/polygerrit-ui/app/embed/diff-old/gr-diff/gr-diff.ts
+++ b/polygerrit-ui/app/embed/diff-old/gr-diff/gr-diff.ts
@@ -374,6 +374,7 @@
 
   private renderContainer() {
     const cssClasses = {
+      oldDiff: true,
       diffContainer: true,
       unified: this.viewMode === DiffViewMode.UNIFIED,
       sideBySide: this.viewMode === DiffViewMode.SIDE_BY_SIDE,
diff --git a/polygerrit-ui/app/embed/diff-old/gr-diff/gr-diff_test.ts b/polygerrit-ui/app/embed/diff-old/gr-diff/gr-diff_test.ts
index 645a64a..af3a492 100644
--- a/polygerrit-ui/app/embed/diff-old/gr-diff/gr-diff_test.ts
+++ b/polygerrit-ui/app/embed/diff-old/gr-diff/gr-diff_test.ts
@@ -61,7 +61,7 @@
       assert.shadowDom.equal(
         element,
         /* HTML */ `
-          <div class="diffContainer sideBySide">
+          <div class="diffContainer oldDiff sideBySide">
             <table id="diffTable"></table>
           </div>
         `
@@ -77,7 +77,7 @@
       assert.shadowDom.equal(
         element,
         /* HTML */ `
-          <div class="diffContainer unified">
+          <div class="diffContainer oldDiff unified">
             <table class="selected-right" id="diffTable">
               <colgroup>
                 <col class="blame gr-diff" />
@@ -1343,7 +1343,7 @@
       assert.shadowDom.equal(
         element,
         /* HTML */ `
-          <div class="diffContainer sideBySide">
+          <div class="diffContainer oldDiff sideBySide">
             <table class="selected-right" id="diffTable">
               <colgroup>
                 <col class="blame gr-diff" />
@@ -3141,7 +3141,7 @@
         assert.shadowDom.equal(
           element,
           /* HTML */ `
-            <div class="diffContainer sideBySide">
+            <div class="diffContainer oldDiff sideBySide">
               <gr-diff-section class="left-FILE right-FILE"> </gr-diff-section>
               <gr-diff-row class="left-FILE right-FILE"> </gr-diff-row>
               <table class="selected-right" id="diffTable">
diff --git a/polygerrit-ui/app/embed/diff/gr-diff/gr-diff.ts b/polygerrit-ui/app/embed/diff/gr-diff/gr-diff.ts
index cc49b61..42cffdb 100644
--- a/polygerrit-ui/app/embed/diff/gr-diff/gr-diff.ts
+++ b/polygerrit-ui/app/embed/diff/gr-diff/gr-diff.ts
@@ -461,6 +461,7 @@
 
   private renderContainer() {
     const cssClasses = {
+      newDiff: true,
       diffContainer: true,
       unified: this.viewMode === DiffViewMode.UNIFIED,
       sideBySide: this.viewMode === DiffViewMode.SIDE_BY_SIDE,
diff --git a/polygerrit-ui/app/embed/diff/gr-diff/gr-diff_test.ts b/polygerrit-ui/app/embed/diff/gr-diff/gr-diff_test.ts
index 8806dbf..88682d9 100644
--- a/polygerrit-ui/app/embed/diff/gr-diff/gr-diff_test.ts
+++ b/polygerrit-ui/app/embed/diff/gr-diff/gr-diff_test.ts
@@ -73,7 +73,7 @@
       assert.shadowDom.equal(
         element,
         /* HTML */ `
-          <div class="diffContainer sideBySide">
+          <div class="diffContainer newDiff sideBySide">
             <table id="diffTable">
               <colgroup>
                 <col class="blame gr-diff" />
@@ -99,7 +99,7 @@
       assert.shadowDom.equal(
         element,
         /* HTML */ `
-          <div class="diffContainer unified">
+          <div class="diffContainer newDiff unified">
             <table class="selected-right" id="diffTable">
               <colgroup>
                 <col class="blame gr-diff" />
@@ -1365,7 +1365,7 @@
       assert.shadowDom.equal(
         element,
         /* HTML */ `
-          <div class="diffContainer sideBySide">
+          <div class="diffContainer newDiff sideBySide">
             <table class="selected-right" id="diffTable">
               <colgroup>
                 <col class="blame gr-diff" />
@@ -3157,7 +3157,7 @@
         assert.shadowDom.equal(
           element,
           /* HTML */ `
-            <div class="diffContainer sideBySide">
+            <div class="diffContainer newDiff sideBySide">
               <gr-diff-section class="left-FILE right-FILE"> </gr-diff-section>
               <gr-diff-row class="left-FILE right-FILE"> </gr-diff-row>
               <table class="selected-right" id="diffTable">