Initial support for emitting unwinding information in perf jitdump.

src/arm/assembler-arm.cc

Index: src/arm/assembler-arm.cc
diff --git a/src/arm/assembler-arm.cc b/src/arm/assembler-arm.cc
index 154e69be7fccc17eb9a144ebad540e87164a9a0d..9633a63ea9f7c95011221e899e4bac8f38c34913 100644
--- a/src/arm/assembler-arm.cc
+++ b/src/arm/assembler-arm.cc
@@ -517,6 +517,8 @@ void Assembler::GetCode(CodeDesc* desc) {
   desc->constant_pool_size =
       (constant_pool_offset ? desc->instr_size - constant_pool_offset : 0);
   desc->origin = this;
+  desc->unwinding_info_size = 0;
+  desc->unwinding_info = nullptr;
 }