Kernel+SystemMonitor: Add fault counters

This patch adds three separate per-process fault counters:

- Inode faults

    An inode fault happens when we've memory-mapped a file from disk
    and we end up having to load 1 page (4KB) of the file into memory.

- Zero faults

    Memory returned by mmap() is lazily zeroed out. Every time we have
    to zero out 1 page, we count a zero fault.

- CoW faults

    VM objects can be shared by multiple mappings that make their own
    unique copy iff they want to modify it. The typical reason here is
    memory shared between a parent and child process.

Kernel/Process.h

@@ -291,6 +291,12 @@ public:
 
     unsigned syscall_count() const { return m_syscall_count; }
     void did_syscall() { ++m_syscall_count; }
+    unsigned inode_faults() const { return m_inode_faults; }
+    void did_inode_fault() { ++m_inode_faults; }
+    unsigned zero_faults() const { return m_zero_faults; }
+    void did_zero_fault() { ++m_zero_faults; }
+    unsigned cow_faults() const { return m_cow_faults; }
+    void did_cow_fault() { ++m_cow_faults; }
 
     const ELFLoader* elf_loader() const { return m_elf_loader.ptr(); }
 
@@ -369,6 +375,9 @@ private:
     int m_next_tid { 0 };
 
     unsigned m_syscall_count { 0 };
+    unsigned m_inode_faults { 0 };
+    unsigned m_zero_faults { 0 };
+    unsigned m_cow_faults { 0 };
 
     RefPtr<ProcessTracer> m_tracer;
     OwnPtr<ELFLoader> m_elf_loader;