Fix profiling on ARM64.

runtime/vm/signal_handler_android.cc

Index: runtime/vm/signal_handler_android.cc
diff --git a/runtime/vm/signal_handler_android.cc b/runtime/vm/signal_handler_android.cc
index 65407511ec9fe28e1defb2e4f85882a7f9e7898c..a85dbb78a4d31dc1f867008bbac8675b36d7d77b 100644
--- a/runtime/vm/signal_handler_android.cc
+++ b/runtime/vm/signal_handler_android.cc
@@ -66,7 +66,7 @@ uintptr_t SignalHandler::GetDartStackPointer(const mcontext_t& mcontext) {
 #elif defined(HOST_ARCH_ARM)
   sp = static_cast<uintptr_t>(mcontext.arm_sp);
 #elif defined(HOST_ARCH_ARM64)
-  sp = static_cast<uintptr_t>(mcontext.regs[18]);
+  sp = static_cast<uintptr_t>(mcontext.regs[19]);

[Cutch, 2015/10/30 02:29:57]

Could we add #define for the register in constants_??.h  and use that here
instead of the number?

[rmacnak, 2015/10/30 16:17:41]

constants_??.h is included for the target architecture, but not host.

 #else
 #error Unsupported architecture.
 #endif  // HOST_ARCH_...