Add comment re. Opera bug.

d3.layout.js

@@ -113,16 +113,19 @@ d3.layout.chord = function() {
     k = (2 * Math.PI - padding * n) / k;
 
     // Compute the start and end angle for each group and subgroup.
+    // Note: Opera has a bug reordering object literal properties!
     x = 0, i = -1; while (++i < n) {
       x0 = x, j = -1; while (++j < n) {
         var di = groupIndex[i],
             dj = subgroupIndex[di][j],
-            v = matrix[di][dj];
+            v = matrix[di][dj],
+            a0 = x,
+            a1 = x += v * k;
         subgroups[di + "-" + dj] = {
           index: di,
           subindex: dj,
-          startAngle: x,
-          endAngle: x += v * k,
+          startAngle: a0,
+          endAngle: a1,
           value: v
         };
       }

src/layout/chord.js

@@ -55,19 +55,21 @@ d3.layout.chord = function() {
     k = (2 * Math.PI - padding * n) / k;
 
     // Compute the start and end angle for each group and subgroup.
+    // Note: Opera has a bug reordering object literal properties!
     x = 0, i = -1; while (++i < n) {
       x0 = x, j = -1; while (++j < n) {
         var di = groupIndex[i],
             dj = subgroupIndex[di][j],
-            v = matrix[di][dj];
+            v = matrix[di][dj],
+            a0 = x,
+            a1 = x += v * k;
         subgroups[di + "-" + dj] = {
           index: di,
           subindex: dj,
-          startAngle: x,
-          endAngle: x + v * k,
+          startAngle: a0,
+          endAngle: a1,
           value: v
         };
-        x += v * k;
       }
       groups.push({
         index: di,