Revert of [tracing] Turn StackFrame into struct.

base/trace_event/heap_profiler_heap_dump_writer.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_heap_dump_writer.h"
 
 #include <stdint.h>
 
 #include <algorithm>
 #include <iterator>
@@ skipping 56 matching lines @@
 
 // Comparison operator to order buckets by their size.
 bool operator<(const Bucket& lhs, const Bucket& rhs) {
   return lhs.size < rhs.size;
 }
 
 // Groups the allocations in the bucket by |breakBy|. The buckets in the
 // returned list will have |backtrace_cursor| advanced or
 // |is_broken_down_by_type_name| set depending on the property to group by.
 std::vector<Bucket> GetSubbuckets(const Bucket& bucket, BreakDownMode breakBy) {
-  base::hash_map<const void*, Bucket> breakdown;
+  base::hash_map<const char*, Bucket> breakdown;
 
   if (breakBy == BreakDownMode::kByBacktrace) {
     for (const auto& context_and_metrics : bucket.metrics_by_context) {
       const Backtrace& backtrace = context_and_metrics.first->backtrace;
-      const StackFrame* begin = std::begin(backtrace.frames);
-      const StackFrame* end = begin + backtrace.frame_count;
-      const StackFrame* cursor = begin + bucket.backtrace_cursor;
+      const char* const* begin = std::begin(backtrace.frames);
+      const char* const* end = std::end(backtrace.frames);
+      const char* const* cursor = begin + bucket.backtrace_cursor;
+
+      // The backtrace in the context is padded with null pointers, but these
+      // should not be considered for breakdown. Adjust end to point past the
+      // last non-null frame.
+      while (begin != end && *(end - 1) == nullptr)
+        end--;
 
       DCHECK_LE(cursor, end);
 
       if (cursor != end) {
-        Bucket& subbucket = breakdown[cursor->value];
+        Bucket& subbucket = breakdown[*cursor];
         subbucket.size += context_and_metrics.second.size;
         subbucket.count += context_and_metrics.second.count;
         subbucket.metrics_by_context.push_back(context_and_metrics);
         subbucket.backtrace_cursor = bucket.backtrace_cursor + 1;
         subbucket.is_broken_down_by_type_name =
             bucket.is_broken_down_by_type_name;
         DCHECK_GT(subbucket.size, 0u);
         DCHECK_GT(subbucket.count, 0u);
       }
     }
@@ skipping 82 matching lines @@
 HeapDumpWriter::~HeapDumpWriter() {}
 
 bool HeapDumpWriter::AddEntryForBucket(const Bucket& bucket) {
   // The contexts in the bucket are all different, but the [begin, cursor) range
   // is equal for all contexts in the bucket, and the type names are the same if
   // |is_broken_down_by_type_name| is set.
   DCHECK(!bucket.metrics_by_context.empty());
 
   const AllocationContext* context = bucket.metrics_by_context.front().first;
 
-  const StackFrame* backtrace_begin = std::begin(context->backtrace.frames);
-  const StackFrame* backtrace_end = backtrace_begin + bucket.backtrace_cursor;
+  const char* const* backtrace_begin = std::begin(context->backtrace.frames);
+  const char* const* backtrace_end = backtrace_begin + bucket.backtrace_cursor;
   DCHECK_LE(bucket.backtrace_cursor, arraysize(context->backtrace.frames));
 
   Entry entry;
-  entry.stack_frame_id = stack_frame_deduplicator_->Insert(
-      backtrace_begin, backtrace_end);
+  entry.stack_frame_id =
+      stack_frame_deduplicator_->Insert(backtrace_begin, backtrace_end);
 
   // Deduplicate the type name, or use ID -1 if type name is not set.
   entry.type_id = bucket.is_broken_down_by_type_name
                       ? type_name_deduplicator_->Insert(context->type_name)
                       : -1;
 
   entry.size = bucket.size;
   entry.count = bucket.count;
 
   auto position_and_inserted = entries_.insert(entry);
@@ skipping 91 matching lines @@
     const hash_map<AllocationContext, AllocationMetrics>& metrics_by_context,
     StackFrameDeduplicator* stack_frame_deduplicator,
     TypeNameDeduplicator* type_name_deduplicator) {
   internal::HeapDumpWriter writer(stack_frame_deduplicator,
                                   type_name_deduplicator);
   return Serialize(writer.Summarize(metrics_by_context));
 }
 
 }  // namespace trace_event
 }  // namespace base