Add methods to enable configuration of ResourceConstraints based on limits derived at runtime.

src/platform-openbsd.cc

Index: src/platform-openbsd.cc
diff --git a/src/platform-openbsd.cc b/src/platform-openbsd.cc
index 4f5420ee45c97e5ede7ee0cde34118f1aac7c947..0b6c2bce7b00fe3e233cafede45b924b87cc483c 100644
--- a/src/platform-openbsd.cc
+++ b/src/platform-openbsd.cc
@@ -231,6 +231,16 @@ void OS::SignalCodeMovingGC() {
 }
 
 
+uintptr_t OS::TotalPhysicalMemory(int pages_name) {
+  intptr_t pages = sysconf(pages_name);
+  intptr_t page_size = sysconf(_SC_PAGESIZE);
+  if (pages == -1 || page_size == -1) {
+    UNREACHABLE();
+    return 0;
+  }
+  return static_cast<uintptr_t>(pages) * page_size;
+}
+
 
 // Constants used for mmap.
 static const int kMmapFd = -1;