tracing: split out ThreadLocalEventBuffer

base/trace_event/trace_buffer.h

Index: base/trace_event/trace_buffer.h
diff --git a/base/trace_event/trace_buffer.h b/base/trace_event/trace_buffer.h
index 4885a3c7c0931b829cda6207808c378c09463e8e..369e481e63a5c23a1119a41e742ebd0c21e48dd6 100644
--- a/base/trace_event/trace_buffer.h
+++ b/base/trace_event/trace_buffer.h
@@ -8,6 +8,8 @@
 #include <stddef.h>
 #include <stdint.h>
 
+#include <limits>
+
 #include "base/base_export.h"
 #include "base/trace_event/trace_event.h"
 #include "base/trace_event/trace_event_impl.h"
@@ -19,6 +21,12 @@ namespace trace_event {
 // TraceBufferChunk is the basic unit of TraceBuffer.
 class BASE_EXPORT TraceBufferChunk {
  public:
+  // These values must be kept consistent with the numbers of bits of
+  // chunk_index and event_index fields in TraceEventHandle
+  // (in trace_event_impl.h).
+  static const size_t kMaxChunkIndex = (1u << 26) - 1;
+  static const size_t kTraceBufferChunkSize = 64;
+
   explicit TraceBufferChunk(uint32_t seq);
   ~TraceBufferChunk();
 
@@ -39,13 +47,19 @@ class BASE_EXPORT TraceBufferChunk {
     return &chunk_[index];
   }
 
-  void EstimateTraceMemoryOverhead(TraceEventMemoryOverhead* overhead);
+  void MakeHandle(size_t chunk_index,
+                  size_t event_index,
+                  TraceEventHandle* handle) {
+    DCHECK(seq_);
+    DCHECK(chunk_index <= kMaxChunkIndex);
+    DCHECK(event_index < kTraceBufferChunkSize);
+    DCHECK(chunk_index <= std::numeric_limits<uint16_t>::max());
+    handle->chunk_seq = seq_;
+    handle->chunk_index = static_cast<uint16_t>(chunk_index);
+    handle->event_index = static_cast<uint16_t>(event_index);
+  }
 
-  // These values must be kept consistent with the numbers of bits of
-  // chunk_index and event_index fields in TraceEventHandle
-  // (in trace_event_impl.h).
-  static const size_t kMaxChunkIndex = (1u << 26) - 1;
-  static const size_t kTraceBufferChunkSize = 64;
+  void EstimateTraceMemoryOverhead(TraceEventMemoryOverhead* overhead);
 
  private:
   size_t next_free_;