Fix cctest/test-unboxed-doubles/IncrementalWriteBarrierObjectShiftFieldsRight after 5e87a0.

Make sure that when manual evacuation candidate selection is enabled we do not select more pages than requested.
BUG=

TBR=hpayer@chromium.org

Review URL: https://codereview.chromium.org/1157293002

Cr-Commit-Position: refs/heads/master@{#28662}

src/heap/mark-compact.cc

@@ -678,18 +678,25 @@ void MarkCompactCollector::CollectEvacuationCandidates(PagedSpace* space) {
       reduce_memory_footprint_ ||
       heap()->HasLowAllocationRate(
           heap()->tracer()->CurrentAllocationThroughputInBytesPerMillisecond());
-
-  if (FLAG_stress_compaction || FLAG_manual_evacuation_candidates_selection) {
+  if (FLAG_manual_evacuation_candidates_selection) {
     for (size_t i = 0; i < pages.size(); i++) {
       Page* p = pages[i].second;
-      if (((i % 2 == 0) && FLAG_stress_compaction) ||
-          p->IsFlagSet(MemoryChunk::FORCE_EVACUATION_CANDIDATE_FOR_TESTING)) {
+      if (p->IsFlagSet(MemoryChunk::FORCE_EVACUATION_CANDIDATE_FOR_TESTING)) {
         candidate_count++;
         total_live_bytes += pages[i].first;
         p->ClearFlag(MemoryChunk::FORCE_EVACUATION_CANDIDATE_FOR_TESTING);
         AddEvacuationCandidate(p);
       }
     }
+  } else if (FLAG_stress_compaction) {
+    for (size_t i = 0; i < pages.size(); i++) {
+      Page* p = pages[i].second;
+      if (i % 2 == 0) {
+        candidate_count++;
+        total_live_bytes += pages[i].first;
+        AddEvacuationCandidate(p);
+      }
+    }
   } else {
     const int kTargetFragmentationPercent = 50;
     const int kMaxEvacuatedBytes = 4 * Page::kPageSize;