Make object accessors more const-correct.

Getting closer to making our IsFOO and FOO::cast methods const-correct...

R=bmeurer@chromium.org

Review URL: https://codereview.chromium.org/349623002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21897 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/spaces.h

@@ -283,6 +283,10 @@ class MemoryChunk {
   static MemoryChunk* FromAddress(Address a) {
     return reinterpret_cast<MemoryChunk*>(OffsetFrom(a) & ~kAlignmentMask);
   }
+  static const MemoryChunk* FromAddress(const byte* a) {
+    return reinterpret_cast<const MemoryChunk*>(
+        OffsetFrom(a) & ~kAlignmentMask);
+  }
 
   // Only works for addresses in pointer spaces, not data or code spaces.
   static inline MemoryChunk* FromAnyPointerAddress(Heap* heap, Address addr);
@@ -627,7 +631,7 @@ class MemoryChunk {
   void InsertAfter(MemoryChunk* other);
   void Unlink();
 
-  inline Heap* heap() { return heap_; }
+  inline Heap* heap() const { return heap_; }
 
   static const int kFlagsOffset = kPointerSize;