VM: Don't do free("") in shutdown when we can't find the cpu model field in /proc/cpuinfo.

runtime/vm/cpuinfo_linux.cc

Index: runtime/vm/cpuinfo_linux.cc
diff --git a/runtime/vm/cpuinfo_linux.cc b/runtime/vm/cpuinfo_linux.cc
index 0341530ae220590056a8e8a4131a9bc2634cde9a..e58bac1fe6a0d5f2f6bb953a6904038386854b8b 100644
--- a/runtime/vm/cpuinfo_linux.cc
+++ b/runtime/vm/cpuinfo_linux.cc
@@ -28,14 +28,20 @@ void CpuInfo::InitOnce() {
   fields_[kCpuInfoFeatures] = "flags";
   method_ = kCpuInfoCpuId;
   CpuId::InitOnce();
-#elif defined(HOST_ARCH_ARM) || defined(HOST_ARCH_ARM64)
-  // TODO(zra): Verify that these field names are correct for arm64.
+#elif defined(HOST_ARCH_ARM)
   fields_[kCpuInfoProcessor] = "Processor";
   fields_[kCpuInfoModel] = "model name";
   fields_[kCpuInfoHardware] = "Hardware";
   fields_[kCpuInfoFeatures] = "Features";
   method_ = kCpuInfoSystem;
   ProcCpuInfo::InitOnce();
+#elif defined(HOST_ARCH_ARM64)
+  fields_[kCpuInfoProcessor] = "Processor";
+  fields_[kCpuInfoModel] = "CPU implementer";
+  fields_[kCpuInfoHardware] = "CPU implementer";
+  fields_[kCpuInfoFeatures] = "Features";
+  method_ = kCpuInfoSystem;
+  ProcCpuInfo::InitOnce();
 #elif defined(HOST_ARCH_MIPS)
   fields_[kCpuInfoProcessor] = "system type";
   fields_[kCpuInfoModel] = "cpu model";