Added missing constants. (#922)

Author: tim-weis

src/um/pdh.rs

@@ -10,6 +10,10 @@ use shared::guiddef::GUID;
 use shared::minwindef::{BOOL, DWORD, FILETIME, LPDWORD, UCHAR};
 use shared::windef::HWND;
 use um::winnt::{BOOLEAN, HANDLE, LONG, LONGLONG, LPCSTR, LPCWSTR, LPSTR, LPWSTR};
+pub const PDH_MAX_COUNTER_NAME: usize = 1024;
+pub const PDH_MAX_INSTANCE_NAME: usize = 1024;
+pub const PDH_MAX_COUNTER_PATH: usize = 2048;
+pub const PDH_MAX_DATASOURCE_PATH: usize = 1024;
 pub const PDH_FMT_RAW: DWORD = 0x00000010;
 pub const PDH_FMT_ANSI: DWORD = 0x00000020;
 pub const PDH_FMT_UNICODE: DWORD = 0x00000040;