[tracing] Turn StackFrame into struct.

base/trace_event/heap_profiler_allocation_context_tracker.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/trace_event/heap_profiler_allocation_context_tracker.h"
 
 #include <algorithm>
 #include <iterator>
 
 #include "base/atomicops.h"
@@ skipping 57 matching lines @@
   // When enabling capturing, also initialize the TLS slot. This does not create
   // a TLS instance yet.
   if (enabled && !g_tls_alloc_ctx_tracker.initialized())
     g_tls_alloc_ctx_tracker.Initialize(DestructAllocationContextTracker);
 
   // Release ordering ensures that when a thread observes |capture_enabled_| to
   // be true through an acquire load, the TLS slot has been initialized.
   subtle::Release_Store(&capture_enabled_, enabled);
 }
 
-void AllocationContextTracker::PushPseudoStackFrame(StackFrame frame) {
+void AllocationContextTracker::PushPseudoStackFrame(
+    const char* trace_event_name) {
   // Impose a limit on the height to verify that every push is popped, because
   // in practice the pseudo stack never grows higher than ~20 frames.
   if (pseudo_stack_.size() < kMaxStackDepth)
-    pseudo_stack_.push_back(frame);
+    pseudo_stack_.push_back(trace_event_name);
   else
     NOTREACHED();
 }
 
-// static
-void AllocationContextTracker::PopPseudoStackFrame(StackFrame frame) {
+void AllocationContextTracker::PopPseudoStackFrame(
+    const char* trace_event_name) {
   // Guard for stack underflow. If tracing was started with a TRACE_EVENT in
   // scope, the frame was never pushed, so it is possible that pop is called
   // on an empty stack.
   if (pseudo_stack_.empty())
     return;
 
   // Assert that pushes and pops are nested correctly. This DCHECK can be
   // hit if some TRACE_EVENT macro is unbalanced (a TRACE_EVENT_END* call
   // without a corresponding TRACE_EVENT_BEGIN).
-  DCHECK_EQ(frame, pseudo_stack_.back())
+  DCHECK_EQ(trace_event_name, pseudo_stack_.back())
       << "Encountered an unmatched TRACE_EVENT_END";
 
   pseudo_stack_.pop_back();
 }
 
 void AllocationContextTracker::PushCurrentTaskContext(const char* context) {
   DCHECK(context);
   if (task_contexts_.size() < kMaxTaskDepth)
     task_contexts_.push_back(context);
   else
     NOTREACHED();
 }
 
 void AllocationContextTracker::PopCurrentTaskContext(const char* context) {
   DCHECK_EQ(context, task_contexts_.back())
       << "Encountered an unmatched context end";
   task_contexts_.pop_back();
 }
 
 // static
 AllocationContext AllocationContextTracker::GetContextSnapshot() {
   AllocationContext ctx;
 
   // Fill the backtrace.
   {
-    auto src = pseudo_stack_.begin();
-    auto dst = std::begin(ctx.backtrace.frames);
-    auto src_end = pseudo_stack_.end();
-    auto dst_end = std::end(ctx.backtrace.frames);
+    auto backtrace = std::begin(ctx.backtrace.frames);
+    auto backtrace_end = std::end(ctx.backtrace.frames);
 
-    // Add the thread name as the first enrty in the backtrace.
+    // Add the thread name as the first entry
     if (thread_name_) {
-      DCHECK(dst < dst_end);
-      *dst = thread_name_;
-      ++dst;
+      *backtrace++ = StackFrame::FromThreadName(thread_name_);
     }
 
-    // Copy as much of the bottom of the pseudo stack into the backtrace as
-    // possible.
-    for (; src != src_end && dst != dst_end; src++, dst++)
-      *dst = *src;
+    for (const auto& event_name: pseudo_stack_) {

[Primiano Tucci (use gerrit), 2016/04/19 19:45:06]

to be honest this would probably be more readable if you did just
s/const auto& event_name/const char* event_name/ 

[Dmitry Skiba, 2016/04/19 22:14:14]

Done.

+      if (backtrace == backtrace_end) {
+        break;
+      }
+      *backtrace++ = StackFrame::FromTraceEventName(event_name);
+    }
 
-    // If there is room for more, fill the remaining slots with empty frames.
-    std::fill(dst, dst_end, nullptr);
+    ctx.backtrace.frame_count = backtrace - std::begin(ctx.backtrace.frames);
   }
 
   // TODO(ssid): Fix crbug.com/594803 to add file name as 3rd dimension
   // (component name) in the heap profiler and not piggy back on the type name.
   ctx.type_name = task_contexts_.empty() ? nullptr : task_contexts_.back();
 
   return ctx;
 }
 
 }  // namespace trace_event
 }  // namespace base