A64: Move veneer emission checking in the Assembler.

src/a64/assembler-a64-inl.h

Index: src/a64/assembler-a64-inl.h
diff --git a/src/a64/assembler-a64-inl.h b/src/a64/assembler-a64-inl.h
index e68dee073822f0c56e03b05c19ec44a35f305951..090a4cf0fd8a0f01dd00d08ac5787107800351b1 100644
--- a/src/a64/assembler-a64-inl.h
+++ b/src/a64/assembler-a64-inl.h
@@ -1178,7 +1178,10 @@ inline void Assembler::CheckBuffer() {
   if (buffer_space() < kGap) {
     GrowBuffer();
   }
-  if (pc_offset() >= next_buffer_check_) {
+  if (pc_offset() >= next_veneer_pool_check_) {
+    CheckVeneerPool(false, true);
+  }
+  if (pc_offset() >= next_constant_pool_check_) {
     CheckConstPool(false, true);
   }
 }