[tracing] Add a memory dump provider for DOM storage

content/browser/dom_storage/dom_storage_area.cc

Index: content/browser/dom_storage/dom_storage_area.cc
diff --git a/content/browser/dom_storage/dom_storage_area.cc b/content/browser/dom_storage/dom_storage_area.cc
index 50ef7ff05f993f4ca0bc2b59aa849b9a23c78f35..9fa350719a176240d1c59050eed507d2a7390741 100644
--- a/content/browser/dom_storage/dom_storage_area.cc
+++ b/content/browser/dom_storage/dom_storage_area.cc
@@ -5,14 +5,18 @@
 #include "content/browser/dom_storage/dom_storage_area.h"
 
 #include <algorithm>
+#include <cctype>  // for std::isalnum
 
 #include "base/bind.h"
 #include "base/location.h"
 #include "base/logging.h"
 #include "base/metrics/histogram.h"
 #include "base/process/process_info.h"
+#include "base/strings/stringprintf.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/time/time.h"
+#include "base/trace_event/memory_dump_manager.h"
+#include "base/trace_event/process_memory_dump.h"
 #include "content/browser/dom_storage/dom_storage_namespace.h"
 #include "content/browser/dom_storage/dom_storage_task_runner.h"
 #include "content/browser/dom_storage/local_storage_database_adapter.h"
@@ -330,6 +334,29 @@ void DOMStorageArea::Shutdown() {
   DCHECK(success);
 }
 
+void DOMStorageArea::OnMemoryDump(base::trace_event::ProcessMemoryDump* pmd) {
+  if (!map_->bytes_used())
+    return;
+  // Limit the url length to 50 and strip special characters.
+  std::string url = origin_.spec().substr(0, 50);
+  for (size_t index = 0; index < url.size(); ++index) {
+    if (!std::isalnum(url[index]))
+      url[index] = '_';
+  }
+  std::string name = StringPrintf("dom_storage/%s/%p", url.c_str(), this);

[Primiano Tucci (use gerrit), 2016/04/22 09:56:39]

I'd probably %s_%p instead of %s/%p just for the sake of avoiding one extra
level with one leaf only in the UI

[ssid, 2016/04/22 23:28:16]

No, I intended to make this %s/%p since it groups the usage by sites. it looks
ugly if I write %s_%p. 
There would be multiple 
google_com_0x23
google_com_0x23
google_com_0x45.

+  auto mad = pmd->CreateAllocatorDump(name + "/storage_map");
+  mad->AddScalar(base::trace_event::MemoryAllocatorDump::kNameSize,
+                 base::trace_event::MemoryAllocatorDump::kUnitsBytes,
+                 map_->bytes_used());
+
+  const char* system_allocator_name =
+      base::trace_event::MemoryDumpManager::GetInstance()
+          ->system_allocator_pool_name();
+  if (system_allocator_name)
+    pmd->AddSuballocation(mad->guid(), system_allocator_name);
+  // TODO(ssid): Add memory usage of backing storage crbug.com/605785.
+}
+
 void DOMStorageArea::InitialImportIfNeeded() {
   if (is_initial_import_done_)
     return;