Handle zero-size allocations properly in heap profiler

base/trace_event/heap_profiler_heap_dump_writer.cc

Index: base/trace_event/heap_profiler_heap_dump_writer.cc
diff --git a/base/trace_event/heap_profiler_heap_dump_writer.cc b/base/trace_event/heap_profiler_heap_dump_writer.cc
index b94c31246b9d347d42c285d04878c586ed7f9163..ee48a69c6a39686b0cc0130660ec1364d489f058 100644
--- a/base/trace_event/heap_profiler_heap_dump_writer.cc
+++ b/base/trace_event/heap_profiler_heap_dump_writer.cc
@@ -135,14 +135,10 @@ std::vector<Bucket> BreakDownBy(const Bucket& bucket, BreakDownMode breakBy) {
   size_t accounted_for = 0;
   std::vector<Bucket>::iterator it;
   for (it = buckets.end(); it != buckets.begin(); --it) {
-    // Compute the contribution to the number of bytes accounted for as a
-    // fraction of 125 (in increments of 0.8 percent). Anything less than 1/125
-    // is rounded down to 0 due to integer division. Buckets are iterated by
-    // descending size, so later buckets cannot have a larger contribution than
-    // this one.
+    // Compute the total accounted amount of bytes
+    // If next bucket increase this amount by less then 0.8% just skip the tail

[Primiano Tucci (use gerrit), 2016/04/06 08:20:44]

I'd add a "(1/125)" after 0.8% otherwise It's not clear where it comes from.
Also, nit: missing trailing dots.

     accounted_for += buckets.front().size;
-    size_t contribution = buckets.front().size * 125 / accounted_for;
-    if (contribution == 0)
+    if (buckets.front().size < (accounted_for / 125))
       break;
 
     // Put the largest bucket in [begin, it) at |it - 1| and max-heapify
@@ -234,6 +230,7 @@ const std::set<Entry>& HeapDumpWriter::Summarize(
   // contexts stored in |bytes_by_context|.
   Bucket root_bucket;
   for (const auto& context_and_size : bytes_by_context) {
+    DCHECK_GT(context_and_size.second, 0u);
     const AllocationContext* context = &context_and_size.first;
     const size_t size = context_and_size.second;
     root_bucket.bytes_by_context.push_back(std::make_pair(context, size));