Initial support for emitting unwinding information in perf jitdump.

src/mips64/assembler-mips64.cc

Index: src/mips64/assembler-mips64.cc
diff --git a/src/mips64/assembler-mips64.cc b/src/mips64/assembler-mips64.cc
index bd4e3e225fbee830479f418fe50b641d9c1b9e6e..01004f5dc6f52c2f54e1a690c0675ec1c27fe574 100644
--- a/src/mips64/assembler-mips64.cc
+++ b/src/mips64/assembler-mips64.cc
@@ -300,6 +300,8 @@ void Assembler::GetCode(CodeDesc* desc) {
       static_cast<int>((buffer_ + buffer_size_) - reloc_info_writer.pos());
   desc->origin = this;
   desc->constant_pool_size = 0;
+  desc->unwinding_info_size = 0;
+  desc->unwinding_info = nullptr;
 }