Adds simulator debugger and Stop to arm64.

runtime/vm/assembler_arm64.cc

Index: runtime/vm/assembler_arm64.cc
===================================================================
--- runtime/vm/assembler_arm64.cc	(revision 35109)
+++ runtime/vm/assembler_arm64.cc	(working copy)
@@ -20,7 +20,7 @@
 
 namespace dart {
 
-DEFINE_FLAG(bool, print_stop_message, true, "Print stop message.");
+DEFINE_FLAG(bool, print_stop_message, false, "Print stop message.");
 DECLARE_FLAG(bool, inline_alloc);
 
 
@@ -63,11 +63,6 @@
 }
 
 
-void Assembler::Stop(const char* message) {
-  UNIMPLEMENTED();
-}
-
-
 void Assembler::Emit(int32_t value) {
   AssemblerBuffer::EnsureCapacity ensured(&buffer_);
   buffer_.Emit<int32_t>(value);
@@ -119,6 +114,19 @@
 }
 
 
+void Assembler::Stop(const char* message) {
+  if (FLAG_print_stop_message) {
+    UNIMPLEMENTED();
+  }
+  Label stop;
+  b(&stop);
+  Emit(Utils::Low32Bits(reinterpret_cast<int64_t>(message)));
+  Emit(Utils::High32Bits(reinterpret_cast<int64_t>(message)));
+  Bind(&stop);
+  hlt(kImmExceptionIsDebug);
+}
+
+
 static int CountLeadingZeros(uint64_t value, int width) {
   ASSERT((width == 32) || (width == 64));
   if (value == 0) {