[heap] Fix computation of flags offset in memorychunk

BUG=chromium:581412
LOG=N
R=hpayer@chromium.org

Review URL: https://codereview.chromium.org/1851733002

Cr-Commit-Position: refs/heads/master@{#35189}

src/heap/spaces.h

@@ -478,6 +478,8 @@ class MemoryChunk {
 
   static const intptr_t kSizeOffset = 0;
 
+  static const intptr_t kFlagsOffset = kSizeOffset + kPointerSize;
+
   static const intptr_t kLiveBytesOffset =
       kSizeOffset + kPointerSize  // size_t size
       + kIntptrSize               // intptr_t flags_
@@ -525,8 +527,6 @@ class MemoryChunk {
       kBodyOffset - 1 +
       (kObjectStartAlignment - (kBodyOffset - 1) % kObjectStartAlignment);
 
-  static const int kFlagsOffset = kPointerSize;
-
   // Page size in bytes.  This must be a multiple of the OS page size.
   static const int kPageSize = 1 << kPageSizeBits;
   static const intptr_t kPageAlignmentMask = (1 << kPageSizeBits) - 1;