Make getClassGClayout work with with class types.

Also add an assert to getHeapClassSize to ensure it's not
called in R2R cross-version-bubble.

src/vm/jitinterface.cpp

@@ -1961,6 +1961,10 @@ CEEInfo::getHeapClassSize(
     MethodTable* pMT = VMClsHnd.GetMethodTable();
     _ASSERTE(pMT);
     _ASSERTE(!pMT->IsValueType());
+    _ASSERTE(!pMT->HasComponentSize());
+#ifdef FEATURE_READYTORUN_COMPILER
+    _ASSERTE(!IsReadyToRunCompilation() || pMT->IsInheritanceChainLayoutFixedInCurrentVersionBubble());
+#endif
 
     // Add OBJECT_SIZE to account for method table pointer.
     result = pMT->GetNumInstanceFieldBytes() + OBJECT_SIZE;
@@ -2280,13 +2284,20 @@ unsigned CEEInfo::getClassGClayout (CORINFO_CLASS_HANDLE clsHnd, BYTE* gcPtrs)
     }
     else
     {
-        _ASSERTE(pMT->IsValueType());
         _ASSERTE(sizeof(BYTE) == 1);
 
+        BOOL isValueClass = pMT->IsValueType();
+
+#ifdef FEATURE_READYTORUN_COMPILER
+        _ASSERTE(isValueClass || !IsReadyToRunCompilation() || pMT->IsInheritanceChainLayoutFixedInCurrentVersionBubble());
+#endif
+
+        unsigned int size = isValueClass ? VMClsHnd.GetSize() : pMT->GetNumInstanceFieldBytes() + OBJECT_SIZE;
+
         // assume no GC pointers at first
         result = 0;
         memset(gcPtrs, TYPE_GC_NONE,
-               (VMClsHnd.GetSize() + TARGET_POINTER_SIZE - 1) / TARGET_POINTER_SIZE);
+               (size + TARGET_POINTER_SIZE - 1) / TARGET_POINTER_SIZE);
 
         // walk the GC descriptors, turning on the correct bits
         if (pMT->ContainsPointers())
@@ -2298,7 +2309,8 @@ unsigned CEEInfo::getClassGClayout (CORINFO_CLASS_HANDLE clsHnd, BYTE* gcPtrs)
             {
                 // Get offset into the value class of the first pointer field (includes a +Object)
                 size_t cbSeriesSize = pByValueSeries->GetSeriesSize() + pMT->GetBaseSize();
-                size_t cbOffset = pByValueSeries->GetSeriesOffset() - OBJECT_SIZE;
+                size_t cbSeriesOffset = pByValueSeries->GetSeriesOffset();
+                size_t cbOffset = isValueClass ? cbSeriesOffset - OBJECT_SIZE : cbSeriesOffset;
 
                 _ASSERTE (cbOffset % TARGET_POINTER_SIZE == 0);
                 _ASSERTE (cbSeriesSize % TARGET_POINTER_SIZE == 0);