Get rid of the "spare buffer" cache.

src/x64/assembler-x64.cc

Index: src/x64/assembler-x64.cc
diff --git a/src/x64/assembler-x64.cc b/src/x64/assembler-x64.cc
index 2568cc082204ae839dcf376a416d43b05ed978fb..e428e8ee7771d22360e0aac45e1b2ea53de41b2e 100644
--- a/src/x64/assembler-x64.cc
+++ b/src/x64/assembler-x64.cc
@@ -331,8 +331,8 @@ void Assembler::GrowBuffer() {
 
   // Compute new buffer size.
   CodeDesc desc;  // the new buffer
-  if (buffer_size_ < 4*KB) {
-    desc.buffer_size = 4*KB;
+  if (buffer_size_ == 0) {
+    desc.buffer_size = kMinimalBufferSize;
   } else {
     desc.buffer_size = 2*buffer_size_;
   }
@@ -363,14 +363,7 @@ void Assembler::GrowBuffer() {
   MemMove(rc_delta + reloc_info_writer.pos(), reloc_info_writer.pos(),
           desc.reloc_size);
 
-  // Switch buffers.
-  if (isolate() != NULL &&
-      isolate()->assembler_spare_buffer() == NULL &&
-      buffer_size_ == kMinimalBufferSize) {
-    isolate()->set_assembler_spare_buffer(buffer_);
-  } else {
-    DeleteArray(buffer_);
-  }
+  DeleteArray(buffer_);
   buffer_ = desc.buffer;
   buffer_size_ = desc.buffer_size;
   pc_ += pc_delta;