Initial revision of ARM simulator and (empty) MIPS simulator.

runtime/vm/os_macos.cc

Index: runtime/vm/os_macos.cc
===================================================================
--- runtime/vm/os_macos.cc	(revision 17504)
+++ runtime/vm/os_macos.cc	(working copy)
@@ -123,6 +123,15 @@
 }
 
 
+void OS::DebugBreak() {
+#if defined(HOST_ARCH_X64) || defined(HOST_ARCH_IA32)
+  asm("int $3");
+#else
+#error Unsupported architecture.
+#endif
+}
+
+
 void OS::Print(const char* format, ...) {
   va_list args;
   va_start(args, format);
@@ -186,6 +195,10 @@
 }
 
 
+// Cache the null page size.
+uword OS::null_page_size_ = 0;
+
+
 void OS::InitOnce() {
   // TODO(5411554): For now we check that initonce is called only once,
   // Once there is more formal mechanism to call InitOnce we can move
@@ -193,6 +206,9 @@
   static bool init_once_called = false;
   ASSERT(init_once_called == false);
   init_once_called = true;
+
+  // Initialize the null page size.
+  null_page_size_ = static_cast<uword>(getpagesize());
 }