Add experimental support for tracing the state of the VM heap to a file

src/d8.cc

Index: src/d8.cc
===================================================================
--- src/d8.cc	(revision 9457)
+++ src/d8.cc	(working copy)
@@ -112,6 +112,27 @@
 }
 
 
+class FileHeapVisualizer : public v8::HeapVisualizer {
+ public:
+  explicit FileHeapVisualizer(const char* path) {
+    file_ = i::OS::FOpen(path, "w");
+  }
+
+  ~FileHeapVisualizer() {
+    if (file_ != NULL) fclose(file_);
+  }
+
+  void Write(const char* buf, int len) {
+    fwrite(reinterpret_cast<const void*>(buf), 1, len, file_);
+  }
+
+  bool open_succeeded() { return file_ != NULL; }
+
+ private:
+  FILE* file_;
+};
+
+
 CounterMap* Shell::counter_map_;
 i::OS::MemoryMappedFile* Shell::counters_file_ = NULL;
 CounterCollection Shell::local_counters_;
@@ -635,7 +656,6 @@
 }
 #endif  // V8_SHARED
 
-
 #ifdef COMPRESS_STARTUP_DATA_BZ2
 class BZip2Decompressor : public v8::StartupDataDecompressor {
  public:
@@ -1264,6 +1284,17 @@
       }
 #endif  // V8_SHARED
     }
+
+    if (i::FLAG_trace_heap) {
+      FileHeapVisualizer* visualizer =
+          new FileHeapVisualizer(i::FLAG_trace_heap_file);
+      if (visualizer->open_succeeded()) {
+        RegisterHeapVisualizer(visualizer);
+      } else {
+        delete visualizer;
+      }
+    }
+
     {
       Context::Scope cscope(context);
       options.isolate_sources[0].Execute();