[tracing] Switch to new heap dump format.

base/trace_event/heap_profiler_stack_frame_deduplicator.cc

Index: base/trace_event/heap_profiler_stack_frame_deduplicator.cc
diff --git a/base/trace_event/heap_profiler_stack_frame_deduplicator.cc b/base/trace_event/heap_profiler_stack_frame_deduplicator.cc
index fc5da0d1dde9ed15498e1d03574d737c5f004460..a230c62bf4e71546890ea8a2bf9bbda84ef79ca7 100644
--- a/base/trace_event/heap_profiler_stack_frame_deduplicator.cc
+++ b/base/trace_event/heap_profiler_stack_frame_deduplicator.cc
@@ -11,6 +11,7 @@
 #include <utility>
 
 #include "base/strings/stringprintf.h"
+#include "base/trace_event/heap_profiler_string_deduplicator.h"
 #include "base/trace_event/memory_usage_estimator.h"
 #include "base/trace_event/trace_event_argument.h"
 #include "base/trace_event/trace_event_memory_overhead.h"
@@ -28,11 +29,21 @@ size_t StackFrameDeduplicator::FrameNode::EstimateMemoryUsage() const {
   return base::trace_event::EstimateMemoryUsage(children);
 }
 
-StackFrameDeduplicator::StackFrameDeduplicator() {}
+StackFrameDeduplicator::StackFrameDeduplicator(
+    StringDeduplicator* string_deduplicator)
+    : string_deduplicator_(string_deduplicator), last_exported_index_(0) {
+  // Add implicit entry for id 0 (empty backtraces).
+  frames_.push_back({StackFrame::FromTraceEventName(nullptr), -1});

[Primiano Tucci (use gerrit), 2017/03/09 11:47:44]

you say 0 above but push -1 here? 

[DmitrySkiba, 2017/03/14 22:12:47]

Oh, the joy of unnamed constants :) This -1 means 'no parent'. I replaced it
(and other occurrences) with explicit kInvalidFrameIndex constant.

+}
 StackFrameDeduplicator::~StackFrameDeduplicator() {}
 
 int StackFrameDeduplicator::Insert(const StackFrame* beginFrame,
                                    const StackFrame* endFrame) {
+  if (beginFrame == endFrame) {
+    // Empty backtraces are mapped to id 0.
+    return 0;
+  }
+
   int frame_index = -1;
   std::map<StackFrame, int>* nodes = &roots_;
 
@@ -67,56 +78,43 @@ int StackFrameDeduplicator::Insert(const StackFrame* beginFrame,
   return frame_index;
 }
 
-void StackFrameDeduplicator::AppendAsTraceFormat(std::string* out) const {
-  out->append("{");  // Begin the |stackFrames| dictionary.
-
-  int i = 0;
-  auto frame_node = begin();
-  auto it_end = end();
+void StackFrameDeduplicator::ExportIncrementally(TracedValue* traced_value) {
   std::string stringify_buffer;
 
-  while (frame_node != it_end) {
-    // The |stackFrames| format is a dictionary, not an array, so the
-    // keys are stringified indices. Write the index manually, then use
-    // |TracedValue| to format the object. This is to avoid building the
-    // entire dictionary as a |TracedValue| in memory.
-    SStringPrintf(&stringify_buffer, "\"%d\":", i);
-    out->append(stringify_buffer);
+  for (; last_exported_index_ < frames_.size(); ++last_exported_index_) {
+    const auto& frame_node = frames_[last_exported_index_];
+    traced_value->BeginDictionary();
 
-    std::unique_ptr<TracedValue> frame_node_value(new TracedValue);
-    const StackFrame& frame = frame_node->frame;
+    traced_value->SetInteger("id", last_exported_index_);
+
+    int name_string_id = 0;
+    const StackFrame& frame = frame_node.frame;
     switch (frame.type) {
       case StackFrame::Type::TRACE_EVENT_NAME:
-        frame_node_value->SetString(
-            "name", static_cast<const char*>(frame.value));
+        name_string_id =
+            string_deduplicator_->Insert(static_cast<const char*>(frame.value));
         break;
       case StackFrame::Type::THREAD_NAME:
         SStringPrintf(&stringify_buffer,
                       "[Thread: %s]",
                       static_cast<const char*>(frame.value));
-        frame_node_value->SetString("name", stringify_buffer);
+        name_string_id = string_deduplicator_->Insert(stringify_buffer);
         break;
       case StackFrame::Type::PROGRAM_COUNTER:
         SStringPrintf(&stringify_buffer,
                       "pc:%" PRIxPTR,
                       reinterpret_cast<uintptr_t>(frame.value));
-        frame_node_value->SetString("name", stringify_buffer);
+        name_string_id = string_deduplicator_->Insert(stringify_buffer);
         break;
     }
-    if (frame_node->parent_frame_index >= 0) {
-      SStringPrintf(&stringify_buffer, "%d", frame_node->parent_frame_index);
-      frame_node_value->SetString("parent", stringify_buffer);
-    }
-    frame_node_value->AppendAsTraceFormat(out);
+    traced_value->SetInteger("name_sid", name_string_id);

[Primiano Tucci (use gerrit), 2017/03/09 11:47:44]

see my comment above about shortening these to "n" and "p"  (or similar) to work
around JSON sillyness

 
-    i++;
-    frame_node++;
+    if (frame_node.parent_frame_index >= 0) {
+      traced_value->SetInteger("parent", frame_node.parent_frame_index);
+    }
 
-    if (frame_node != it_end)
-      out->append(",");
+    traced_value->EndDictionary();
   }
-
-  out->append("}");  // End the |stackFrames| dictionary.
 }
 
 void StackFrameDeduplicator::EstimateTraceMemoryOverhead(