Initial support for emitting unwinding information in perf jitdump.

src/mips/assembler-mips.cc

Index: src/mips/assembler-mips.cc
diff --git a/src/mips/assembler-mips.cc b/src/mips/assembler-mips.cc
index 381de5d0e84e0e0586408446ad07a9ff41d02fb7..655105f292c1775a12abaf26c5b33f690c3c575f 100644
--- a/src/mips/assembler-mips.cc
+++ b/src/mips/assembler-mips.cc
@@ -319,6 +319,8 @@ void Assembler::GetCode(CodeDesc* desc) {
   desc->reloc_size = (buffer_ + buffer_size_) - reloc_info_writer.pos();
   desc->origin = this;
   desc->constant_pool_size = 0;
+  desc->unwinding_info_size = 0;
+  desc->unwinding_info = nullptr;
 }