Allocate the fixed-size timeline buffer with virtual memory instead of malloc.

runtime/vm/timeline_win.cc

Index: runtime/vm/timeline_win.cc
diff --git a/runtime/vm/timeline_win.cc b/runtime/vm/timeline_win.cc
index d28a344a89587c55efa257b0c42236a724c05e2b..11f5e73437471df64508b8b6fdca820a82a958a4 100644
--- a/runtime/vm/timeline_win.cc
+++ b/runtime/vm/timeline_win.cc
@@ -33,7 +33,7 @@ TimelineEventBlock* TimelineEventPlatformRecorder::GetNewBlockLocked() {
   if (block_cursor_ == num_blocks_) {
     block_cursor_ = 0;
   }
-  TimelineEventBlock* block = blocks_[block_cursor_++];
+  TimelineEventBlock* block = &blocks_[block_cursor_++];
   block->Reset();
   block->Open();
   return block;