Fix quadratic test in debug-mode ARM64 assembler

src/arm64/assembler-arm64.cc

Index: src/arm64/assembler-arm64.cc
diff --git a/src/arm64/assembler-arm64.cc b/src/arm64/assembler-arm64.cc
index 524be154c53bef81a410c3c648f456fc32f85bd3..bf44c0810e138b729c7cd7f7fbe9ca87ec6517eb 100644
--- a/src/arm64/assembler-arm64.cc
+++ b/src/arm64/assembler-arm64.cc
@@ -603,9 +603,12 @@ void Assembler::Align(int m) {
 void Assembler::CheckLabelLinkChain(Label const * label) {
 #ifdef DEBUG
   if (label->is_linked()) {
+    static const int kMaxLinksToCheck = 256;  // Avoid O(n2) behaviour.
+    int links_checked = 0;
     int linkoffset = label->pos();
     bool end_of_chain = false;
     while (!end_of_chain) {
+      if (++links_checked > kMaxLinksToCheck) break;
       Instruction * link = InstructionAt(linkoffset);
       int linkpcoffset = link->ImmPCOffset();
       int prevlinkoffset = linkoffset + linkpcoffset;