DevTools: Add memory dump provider to SharedFileWatcher

The provider reports number of files currently being monitored by
the watcher. This is needed to confirm there's no memory leak in the
SharedFileWatcher.

BUG=810155

Change-Id: I560a4ce8c7a297cd60162c528e8c76c37f3a47ff
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1539017Reviewed-by: ssid <ssid@chromium.org>
Reviewed-by: Dmitry Gozman <dgozman@chromium.org>
Commit-Queue: Alexei Filippov <alph@chromium.org>
Cr-Commit-Position: refs/heads/master@{#644387}

base/trace_event/memory_infra_background_whitelist.cc

@@ -27,9 +27,10 @@ const char* const kDumpProviderWhitelist[] = {
     "BlinkObjectCounters",
     "BlobStorageContext",
     "ClientDiscardableSharedMemoryManager",
+    "DevTools",
+    "DiscardableSharedMemoryManager",
     "DOMStorage",
     "DownloadService",
-    "DiscardableSharedMemoryManager",
     "gpu::BufferManager",
     "gpu::RenderbufferManager",
     "gpu::TextureManager",
@@ -84,6 +85,7 @@ const char* const kAllocatorDumpNameWhitelist[] = {
     "blink_objects/UACSSResource",
     "blink_objects/ResourceFetcher",
     "components/download/controller_0x?",
+    "devtools/file_watcher_path_count",
     "discardable",
     "discardable/child_0x?",
     "extensions/value_store/Extensions.Database.Open.Settings/0x?",

chrome/browser/devtools/devtools_file_watcher.cc

@@ -19,6 +19,8 @@
 #include "base/sequenced_task_runner.h"
 #include "base/task/lazy_task_runner.h"
 #include "base/threading/sequenced_task_runner_handle.h"
+#include "base/trace_event/memory_dump_manager.h"
+#include "base/trace_event/memory_dump_provider.h"
 #include "content/public/browser/browser_thread.h"
 
 using content::BrowserThread;
@@ -28,8 +30,9 @@ static constexpr int kDefaultThrottleTimeout = 200;
 
 // DevToolsFileWatcher::SharedFileWatcher --------------------------------------
 
-class DevToolsFileWatcher::SharedFileWatcher :
-    public base::RefCounted<SharedFileWatcher> {
+class DevToolsFileWatcher::SharedFileWatcher
+    : public base::RefCounted<SharedFileWatcher>,
+      public base::trace_event::MemoryDumpProvider {
  public:
   SharedFileWatcher();
 
@@ -38,10 +41,14 @@ class DevToolsFileWatcher::SharedFileWatcher :
   void AddWatch(const base::FilePath& path);
   void RemoveWatch(const base::FilePath& path);
 
+  // base::trace_event::MemoryDumpProvider implementation:
+  bool OnMemoryDump(
+      const base::trace_event::MemoryDumpArgs& args,
+      base::trace_event::ProcessMemoryDump* process_memory_dump) override;
+
  private:
-  friend class base::RefCounted<
-      DevToolsFileWatcher::SharedFileWatcher>;
-  ~SharedFileWatcher();
+  friend class base::RefCounted<SharedFileWatcher>;
+  ~SharedFileWatcher() override;
 
   using FilePathTimesMap = std::unordered_map<base::FilePath, base::Time>;
   FilePathTimesMap GetModificationTimes(const base::FilePath& path);
@@ -61,13 +68,31 @@ DevToolsFileWatcher::SharedFileWatcher::SharedFileWatcher()
     : last_dispatch_cost_(
           base::TimeDelta::FromMilliseconds(kDefaultThrottleTimeout)) {
   DevToolsFileWatcher::s_shared_watcher_ = this;
+  base::trace_event::MemoryDumpManager::GetInstance()
+      ->RegisterDumpProviderWithSequencedTaskRunner(
+          this, "DevTools", base::SequencedTaskRunnerHandle::Get(),
+          base::trace_event::MemoryDumpProvider::Options());
 }
 
 DevToolsFileWatcher::SharedFileWatcher::~SharedFileWatcher() {
   DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
+  base::trace_event::MemoryDumpManager::GetInstance()->UnregisterDumpProvider(
+      this);
   DevToolsFileWatcher::s_shared_watcher_ = nullptr;
 }
 
+bool DevToolsFileWatcher::SharedFileWatcher::OnMemoryDump(
+    const base::trace_event::MemoryDumpArgs& args,
+    base::trace_event::ProcessMemoryDump* process_memory_dump) {
+  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
+  auto* dump = process_memory_dump->CreateAllocatorDump(
+      "devtools/file_watcher_path_count");
+  dump->AddScalar(base::trace_event::MemoryAllocatorDump::kNameObjectCount,
+                  base::trace_event::MemoryAllocatorDump::kUnitsObjects,
+                  file_path_times_.size());
+  return true;
+}
+
 void DevToolsFileWatcher::SharedFileWatcher::AddListener(
     DevToolsFileWatcher* watcher) {
   DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
@@ -191,14 +216,12 @@ base::SequencedTaskRunner* impl_task_runner() {
       base::MayBlock(), base::TaskPriority::BEST_EFFORT};
   static base::LazySequencedTaskRunner s_file_task_runner =
       LAZY_SEQUENCED_TASK_RUNNER_INITIALIZER(kImplTaskTraits);
-
   return s_file_task_runner.Get().get();
 }
 }  // namespace
 
 // static
-DevToolsFileWatcher::SharedFileWatcher*
-DevToolsFileWatcher::s_shared_watcher_ = nullptr;
+DevToolsFileWatcher::SharedFileWatcher* DevToolsFileWatcher::s_shared_watcher_;
 
 // static
 void DevToolsFileWatcher::Deleter::operator()(const DevToolsFileWatcher* ptr) {