Heap explorer: Show representation of strings.

* src/profile-generator.cc (V8HeapExplorer::GetSystemEntryName): For
  maps of strings, return a name that encodes the representation
  strategy used for the strings.
  (V8HeapExplorer::ExtractReferences): For strings, visit the maps as
  well, so that the user can see what representation is used for their
  strings.

See http://wingolog.org/pub/string-representations.png for an example of what it looks like.

BUG=

Review URL: https://chromiumcodereview.appspot.com/11344021
Patch from Andy Wingo <wingo@igalia.com>.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@12973 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/profile-generator.cc

@@ -1774,7 +1774,14 @@ void V8HeapExplorer::AddRootEntries(SnapshotFillerInterface* filler) {
 
 const char* V8HeapExplorer::GetSystemEntryName(HeapObject* object) {
   switch (object->map()->instance_type()) {
-    case MAP_TYPE: return "system / Map";
+    case MAP_TYPE:
+      switch (Map::cast(object)->instance_type()) {
+#define MAKE_STRING_MAP_CASE(instance_type, size, name, Name) \
+        case instance_type: return "system / Map (" #Name ")";
+      STRING_TYPE_LIST(MAKE_STRING_MAP_CASE)
+#undef MAKE_STRING_MAP_CASE
+        default: return "system / Map";
+      }
     case JS_GLOBAL_PROPERTY_CELL_TYPE: return "system / JSGlobalPropertyCell";
     case FOREIGN_TYPE: return "system / Foreign";
     case ODDBALL_TYPE: return "system / Oddball";
@@ -1851,7 +1858,6 @@ void V8HeapExplorer::ExtractReferences(HeapObject* obj) {
     ExtractJSObjectReferences(entry, JSObject::cast(obj));
   } else if (obj->IsString()) {
     ExtractStringReferences(entry, String::cast(obj));
-    extract_indexed_refs = false;
   } else if (obj->IsContext()) {
     ExtractContextReferences(entry, Context::cast(obj));
   } else if (obj->IsMap()) {
@@ -1966,11 +1972,14 @@ void V8HeapExplorer::ExtractJSObjectReferences(
 void V8HeapExplorer::ExtractStringReferences(int entry, String* string) {
   if (string->IsConsString()) {
     ConsString* cs = ConsString::cast(string);
-    SetInternalReference(cs, entry, "first", cs->first());
-    SetInternalReference(cs, entry, "second", cs->second());
+    SetInternalReference(cs, entry, "first", cs->first(),
+                         ConsString::kFirstOffset);
+    SetInternalReference(cs, entry, "second", cs->second(),
+                         ConsString::kSecondOffset);
   } else if (string->IsSlicedString()) {
     SlicedString* ss = SlicedString::cast(string);
-    SetInternalReference(ss, entry, "parent", ss->parent());
+    SetInternalReference(ss, entry, "parent", ss->parent(),
+                         SlicedString::kParentOffset);
   }
 }