Fixes for the profiler on arm64.

runtime/vm/signal_handler_android.cc

Index: runtime/vm/signal_handler_android.cc
===================================================================
--- runtime/vm/signal_handler_android.cc	(revision 40496)
+++ runtime/vm/signal_handler_android.cc	(working copy)
@@ -38,7 +38,7 @@
 }
 
 
-uintptr_t SignalHandler::GetStackPointer(const mcontext_t& mcontext) {
+uintptr_t SignalHandler::GetCStackPointer(const mcontext_t& mcontext) {
   uintptr_t sp = 0;
 
 #if defined(TARGET_ARCH_ARM)
@@ -52,6 +52,20 @@
 }
 
 
+uintptr_t SignalHandler::GetDartStackPointer(const mcontext_t& mcontext) {
+  uintptr_t sp = 0;
+
+#if defined(TARGET_ARCH_ARM)
+  sp = static_cast<uintptr_t>(mcontext.arm_sp);
+#elif defined(TARGET_ARCH_ARM64)
+  sp = static_cast<uintptr_t>(mcontext.regs[18]);
+#else
+  UNIMPLEMENTED();
+#endif  // TARGET_ARCH_...
+  return sp;
+}
+
+
 void SignalHandler::Install(SignalAction action) {
   struct sigaction act;
   memset(&act, 0, sizeof(act));