Kernel+SystemMonitor: Expose amount of per-process dirty private memory

Dirty private memory is all memory in non-inode-backed mappings that's
process-private, meaning it's not shared with any other process.

This patch exposes that number via SystemMonitor, giving us an idea of
how much memory each process is responsible for all on its own.

Kernel/VM/InodeVMObject.cpp

@@ -21,6 +21,7 @@ NonnullRefPtr<VMObject> InodeVMObject::clone()
 InodeVMObject::InodeVMObject(Inode& inode)
     : VMObject(inode.size())
     , m_inode(inode)
+    , m_dirty_pages(page_count(), false)
 {
 }
 
@@ -35,6 +36,16 @@ InodeVMObject::~InodeVMObject()
     ASSERT(inode().vmobject() == this);
 }
 
+size_t InodeVMObject::amount_dirty() const
+{
+    size_t count = 0;
+    for (int i = 0; i < m_dirty_pages.size(); ++i) {
+        if (m_dirty_pages.get(i))
+            ++count;
+    }
+    return count * PAGE_SIZE;
+}
+
 void InodeVMObject::inode_size_changed(Badge<Inode>, size_t old_size, size_t new_size)
 {
     dbgprintf("VMObject::inode_size_changed: {%u:%u} %u -> %u\n",
@@ -46,6 +57,8 @@ void InodeVMObject::inode_size_changed(Badge<Inode>, size_t old_size, size_t new
     auto new_page_count = PAGE_ROUND_UP(new_size) / PAGE_SIZE;
     m_physical_pages.resize(new_page_count);
 
+    m_dirty_pages.grow(new_page_count, false);
+
     // FIXME: Consolidate with inode_contents_changed() so we only do a single walk.
     for_each_region([](auto& region) {
         region.remap();