[Interpreter] Change BytecodeLabels to use ZoneLinkedList instead of ZoneVector.

BytecodeList::New() returns a reference to the BytecodeLabel added to the list.
Since ZoneVector can resize, this reference could become invalid. Instead
move to a ZoneLinkedList so the references never move.

Since we were using zone vectors, the old references were still valid, and
they were only mutated to set is_bound_, so only DCHECKs should have been
affected.

Change-Id: I5da850af2596dcd7f56578a6e5badd332350cb5b
Reviewed-on: https://chromium-review.googlesource.com/544941
Commit-Queue: Ross McIlroy <rmcilroy@chromium.org>
Commit-Queue: Tobias Tebbi <tebbi@chromium.org>
Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46145}

src/interpreter/bytecode-label.cc

@@ -13,7 +13,7 @@ namespace interpreter {
 
 BytecodeLabel* BytecodeLabels::New() {
   DCHECK(!is_bound());
-  labels_.push_back(BytecodeLabel());
+  labels_.emplace_back(BytecodeLabel());
   return &labels_.back();
 }
 

src/interpreter/bytecode-label.h

@@ -65,7 +65,7 @@ class V8_EXPORT_PRIVATE BytecodeLabels {
   void BindToLabel(BytecodeArrayBuilder* builder, const BytecodeLabel& target);
 
   bool is_bound() const {
-    bool is_bound = !labels_.empty() && labels_.at(0).is_bound();
+    bool is_bound = !labels_.empty() && labels_.front().is_bound();
     DCHECK(!is_bound ||
            std::all_of(labels_.begin(), labels_.end(),
                        [](const BytecodeLabel& l) { return l.is_bound(); }));
@@ -75,7 +75,7 @@ class V8_EXPORT_PRIVATE BytecodeLabels {
   bool empty() const { return labels_.empty(); }
 
  private:
-  ZoneVector<BytecodeLabel> labels_;
+  ZoneLinkedList<BytecodeLabel> labels_;
 
   DISALLOW_COPY_AND_ASSIGN(BytecodeLabels);
 };