dep/vixl: Add Reset-to-new-buffer overload

dep/vixl/include/vixl/code-buffer-vixl.h

@@ -43,6 +43,7 @@ class CodeBuffer {
   ~CodeBuffer();
 
   void Reset();
+  void Reset(byte* buffer, size_t capacity);
 
 #ifdef VIXL_CODE_BUFFER_MMAP
   void SetExecutable();

dep/vixl/src/code-buffer-vixl.cc

@@ -156,6 +156,11 @@ void CodeBuffer::Reset() {
   SetClean();
 }
 
+void CodeBuffer::Reset(byte* buffer, size_t capacity) {
+  buffer_ = buffer;
+  cursor_ = buffer;
+  capacity_ = capacity;
+}
 
 void CodeBuffer::Grow(size_t new_capacity) {
   VIXL_ASSERT(managed_);