Bug 1932669 - Switch to getpagesize() in Ashmem VolatileBuffer code. r=glandium

This mirrors the OSX code and allows for different Android page sizes.

Differential Revision: https://phabricator.services.mozilla.com/D230320

memory/volatile/VolatileBufferAshmem.cpp

@@ -114,7 +114,8 @@ size_t VolatileBuffer::NonHeapSizeOfExcludingThis() const {
     return 0;
   }
 
-  return (mSize + (PAGE_SIZE - 1)) & PAGE_MASK;
+  size_t pagemask = getpagesize() - 1;
+  return (mSize + pagemask) & ~pagemask;
 }
 
 }  // namespace mozilla