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

runtime/vm/timeline.h

Index: runtime/vm/timeline.h
diff --git a/runtime/vm/timeline.h b/runtime/vm/timeline.h
index 380df4a752569a9f97c164ea6a092f171ce3db19..eecb0dd2f01f06cda623309c41bd44eb42878047 100644
--- a/runtime/vm/timeline.h
+++ b/runtime/vm/timeline.h
@@ -27,6 +27,7 @@ class TimelineEvent;
 class TimelineEventBlock;
 class TimelineEventRecorder;
 class TimelineStream;
+class VirtualMemory;

[zra, 2017/07/27 19:05:44]

Why can't/shouldn't this #include "vm/virtual_memory.h" ?

[rmacnak, 2017/07/27 20:24:33]

It doesn't need it. timeline.h gets included in a lot of places in the VM, and
I'd like to avoid them indirectly including more and more headers.

 class Zone;
 
 // (name, enabled by default for isolate).
@@ -705,7 +706,8 @@ class TimelineEventFixedBufferRecorder : public TimelineEventRecorder {
 
   void PrintJSONEvents(JSONArray* array, TimelineEventFilter* filter);
 
-  TimelineEventBlock** blocks_;
+  VirtualMemory* memory_;
+  TimelineEventBlock* blocks_;
   intptr_t capacity_;
   intptr_t num_blocks_;
   intptr_t block_cursor_;