Bug 1228984 - [css-grid] Auto-placement into columns missed some unoccupied span-1 column slots. r=dholbert

layout/generic/nsGridContainerFrame.cpp

@@ -1534,15 +1534,12 @@ nsGridContainerFrame::FindAutoCol(uint32_t aStartCol, uint32_t aLockedRow,
     // Find the first gap in the current row that's at least 'extent' wide.
     // ('gap' tracks how wide the current column gap is.)
     for (uint32_t j = candidate, gap = 0; j < len && gap < extent; ++j) {
-      ++gap; // tentative, but we may reset it below if a column is occupied
-      if (cellsInRow[j].mIsOccupied) {
-        // Optimization: skip as many occupied cells as we can.
-        do {
-          ++j;
-        } while (j < len && cellsInRow[j].mIsOccupied);
-        candidate = j;
-        gap = 0;
+      if (!cellsInRow[j].mIsOccupied) {
+        ++gap;
+        continue;
       }
+      candidate = j + 1;
+      gap = 0;
     }
     if (lastCandidate < candidate && i != iStart) {
       // Couldn't fit 'extent' tracks at 'lastCandidate' here so we must