Allow property indexes to refer to slots inside the object header.

src/arm/stub-cache-arm.cc

Index: src/arm/stub-cache-arm.cc
diff --git a/src/arm/stub-cache-arm.cc b/src/arm/stub-cache-arm.cc
index 9fc39d4ad8610d4687a758bd56734dd5a6173904..260cdcef0b9f21d813df864eae793f5787d42c80 100644
--- a/src/arm/stub-cache-arm.cc
+++ b/src/arm/stub-cache-arm.cc
@@ -327,18 +327,23 @@ void StubCompiler::GenerateFastPropertyLoad(MacroAssembler* masm,
                                             Register dst,
                                             Register src,
                                             Handle<JSObject> holder,
-                                            int index) {
-  // Adjust for the number of properties stored in the holder.
-  index -= holder->map()->inobject_properties();
-  if (index < 0) {
-    // Get the property straight out of the holder.
-    int offset = holder->map()->instance_size() + (index * kPointerSize);
+                                            PropertyIndex index) {
+  if (index.IsHeaderIndex()) {
+    int offset = index.HeaderIndex() * kPointerSize;
     __ ldr(dst, FieldMemOperand(src, offset));
   } else {
-    // Calculate the offset into the properties array.
-    int offset = index * kPointerSize + FixedArray::kHeaderSize;
-    __ ldr(dst, FieldMemOperand(src, JSObject::kPropertiesOffset));
-    __ ldr(dst, FieldMemOperand(dst, offset));
+    // Adjust for the number of properties stored in the holder.
+    int slot = index.FieldIndex() - holder->map()->inobject_properties();
+    if (slot < 0) {
+      // Get the property straight out of the holder.
+      int offset = holder->map()->instance_size() + (slot * kPointerSize);
+      __ ldr(dst, FieldMemOperand(src, offset));
+    } else {
+      // Calculate the offset into the properties array.
+      int offset = slot * kPointerSize + FixedArray::kHeaderSize;
+      __ ldr(dst, FieldMemOperand(src, JSObject::kPropertiesOffset));
+      __ ldr(dst, FieldMemOperand(dst, offset));
+    }
   }
 }
 
@@ -1196,7 +1201,7 @@ void StubCompiler::GenerateLoadField(Handle<JSObject> object,
                                      Register scratch1,
                                      Register scratch2,
                                      Register scratch3,
-                                     int index,
+                                     PropertyIndex index,
                                      Handle<String> name,
                                      Label* miss) {
   // Check that the receiver isn't a smi.
@@ -1429,7 +1434,7 @@ void StubCompiler::GenerateLoadInterceptor(Handle<JSObject> object,
       // Retrieve a field from field's holder.
       GenerateFastPropertyLoad(masm(), r0, holder_reg,
                                Handle<JSObject>(lookup->holder()),
-                               lookup->GetFieldIndex());
+                               lookup->GetFieldIndex().FieldIndex());
       __ Ret();
     } else {
       // We found CALLBACKS property in prototype chain of interceptor's