Clean up aligned allocation code in preparation for SIMD alignments.

src/heap/spaces.h

Index: src/heap/spaces.h
diff --git a/src/heap/spaces.h b/src/heap/spaces.h
index 9f57ecc3dd92e533ed59cbed048c319b093adf08..7cdb5ba213fdf7035c8830967207764735a6aa71 100644
--- a/src/heap/spaces.h
+++ b/src/heap/spaces.h
@@ -1937,9 +1937,10 @@ class PagedSpace : public Space {
   // address denoted by top in allocation_info_.
   inline HeapObject* AllocateLinearly(int size_in_bytes);
 
-  // Generic fast case allocation function that tries double aligned linear
-  // allocation at the address denoted by top in allocation_info_.
-  inline HeapObject* AllocateLinearlyAligned(int size_in_bytes,
+  // Generic fast case allocation function that tries aligned linear allocation
+  // at the address denoted by top in allocation_info_. Writes the aligned
+  // allocation size, which includes the filler size, to size_in_bytes.
+  inline HeapObject* AllocateLinearlyAligned(int* size_in_bytes,
                                              AllocationAlignment alignment);
 
   // If sweeping is still in progress try to sweep unswept pages. If that is