Kernel+SystemMonitor: Expose amount of per-process clean inode memory

This is memory that's loaded from an inode (file) but not modified in
memory, so still identical to what's on disk. This kind of memory can
be freed and reloaded transparently from disk if needed.

Kernel/VM/InodeVMObject.cpp

@@ -36,6 +36,16 @@ InodeVMObject::~InodeVMObject()
     ASSERT(inode().vmobject() == this);
 }
 
+size_t InodeVMObject::amount_clean() const
+{
+    size_t count = 0;
+    for (int i = 0; i < m_dirty_pages.size(); ++i) {
+        if (!m_dirty_pages.get(i) && m_physical_pages[i])
+            ++count;
+    }
+    return count * PAGE_SIZE;
+}
+
 size_t InodeVMObject::amount_dirty() const
 {
     size_t count = 0;