Fix calculation of live-bytes in pages.

src/spaces.h

Index: src/spaces.h
diff --git a/src/spaces.h b/src/spaces.h
index 051deb4303e94f1be1de3d248fadcc765498c99f..c649b04e385da4dd58cc8fc7ba94246f9b7f9e46 100644
--- a/src/spaces.h
+++ b/src/spaces.h
@@ -265,6 +265,7 @@ class Bitmap {
     }
 
     static bool IsSeq(uint32_t cell) { return cell == 0 || cell == 0xFFFFFFFF; }
+
    private:
     uint32_t seq_start;
     uint32_t seq_type;
@@ -451,12 +452,27 @@ class MemoryChunk {
   // Manage live byte count (count of bytes known to be live,
   // because they are marked black).
   void ResetLiveBytes() {
+    if (FLAG_trace_live_byte_count) {
+      PrintF("ResetLiveBytes:%p:%x->0\n",
+             static_cast<void*>(this), live_byte_count_);
+    }
     live_byte_count_ = 0;
   }
   void IncrementLiveBytes(int by) {
+    ASSERT_LE(static_cast<unsigned>(live_byte_count_), size_);
+    if (FLAG_trace_live_byte_count) {
+      printf("UpdateLiveBytes:%p:%x%c=%x->%x\n",
+             static_cast<void*>(this), live_byte_count_,
+             ((by < 0) ? '-' : '+'), ((by < 0) ? -by : by),
+             live_byte_count_ + by);
+    }
     live_byte_count_ += by;
+    ASSERT_LE(static_cast<unsigned>(live_byte_count_), size_);
+  }
+  int LiveBytes() {
+    ASSERT(static_cast<unsigned>(live_byte_count_) <= size_);
+    return live_byte_count_;
   }
-  int LiveBytes() { return live_byte_count_; }
   static void IncrementLiveBytes(Address address, int by) {
     MemoryChunk::FromAddress(address)->IncrementLiveBytes(by);
   }
@@ -466,10 +482,11 @@ class MemoryChunk {
 
   static const intptr_t kAlignmentMask = kAlignment - 1;
 
+  static const intptr_t kSizeOffset = kPointerSize + kPointerSize;
+
   static const intptr_t kLiveBytesOffset =
-      kPointerSize + kPointerSize + kPointerSize + kPointerSize +
-      kPointerSize + kPointerSize + kPointerSize + kPointerSize +
-      kIntSize;
+      kSizeOffset + kPointerSize + kPointerSize + kPointerSize +
+      kPointerSize + kPointerSize + kPointerSize + kIntSize;
 
   static const size_t kSlotsBufferOffset = kLiveBytesOffset + kIntSize;
 
@@ -699,6 +716,10 @@ class Page : public MemoryChunk {
   void ClearSweptPrecisely() { ClearFlag(WAS_SWEPT_PRECISELY); }
   void ClearSweptConservatively() { ClearFlag(WAS_SWEPT_CONSERVATIVELY); }
 
+#ifdef DEBUG
+  void Print();
+#endif  // DEBUG
+
   friend class MemoryAllocator;
 };