Display histograms from subprocesses in chrome://histograms

chrome/browser/metrics/subprocess_metrics_provider.h

Index: chrome/browser/metrics/subprocess_metrics_provider.h
diff --git a/chrome/browser/metrics/subprocess_metrics_provider.h b/chrome/browser/metrics/subprocess_metrics_provider.h
index d47f5846a3d7438a6aebfbbd1ea8c3d9db98788e..cbdeebb6da794926f3debb0624451a6a4777f459 100644
--- a/chrome/browser/metrics/subprocess_metrics_provider.h
+++ b/chrome/browser/metrics/subprocess_metrics_provider.h
@@ -5,13 +5,14 @@
 #ifndef CHROME_BROWSER_METRICS_SUBPROCESS_METRICS_PROVIDER_H_
 #define CHROME_BROWSER_METRICS_SUBPROCESS_METRICS_PROVIDER_H_
 
+#include <map>
 #include <memory>
-#include <set>
+#include <vector>
 
 #include "base/gtest_prod_util.h"
-#include "base/id_map.h"
+#include "base/metrics/statistics_recorder.h"
 #include "base/scoped_observer.h"
-#include "base/threading/thread_checker.h"
+#include "base/synchronization/lock.h"
 #include "components/metrics/metrics_provider.h"
 #include "content/public/browser/notification_observer.h"
 #include "content/public/browser/notification_registrar.h"
@@ -24,9 +25,11 @@ class SharedPersistentMemoryAllocator;
 
 // SubprocessMetricsProvider gathers and logs histograms stored in shared
 // memory segments between processes.
-class SubprocessMetricsProvider : public metrics::MetricsProvider,
-                                  public content::NotificationObserver,
-                                  public content::RenderProcessHostObserver {
+class SubprocessMetricsProvider
+    : public metrics::MetricsProvider,
+      public base::StatisticsRecorder::MetricsDisplayer,
+      public content::NotificationObserver,
+      public content::RenderProcessHostObserver {
  public:
   SubprocessMetricsProvider();
   ~SubprocessMetricsProvider() override;
@@ -34,6 +37,11 @@ class SubprocessMetricsProvider : public metrics::MetricsProvider,
  private:
   friend class SubprocessMetricsProviderTest;
 
+  enum SnapshotType {
+    SNAPSHOT_DELTA,
+    SNAPSHOT_ABSOLUTE,
+  };
+
   // Indicates subprocess to be monitored with unique id for later reference.
   // Metrics reporting will read histograms from it and upload them to UMA.
   void RegisterSubprocessAllocator(
@@ -44,9 +52,15 @@ class SubprocessMetricsProvider : public metrics::MetricsProvider,
   // allocator it was using.
   void DeregisterSubprocessAllocator(int id);
 
-  // Report all histograms of a given allocator to the snapshot-manager.
+  // Report histograms of a given allocator to the snapshot-manager. If
+  // |query| is not empty, only histograms that contain that string will
+  // be recorded. If |snapshot_type| is ABSOLUTE, no delta from the previous
+  // snapshot will be done. Only one caller, the caller that uploads to UMA,
+  // is allowed to calcuate deltas because they are not independent.
   void RecordHistogramSnapshotsFromAllocator(
       base::HistogramSnapshotManager* snapshot_manager,
+      const std::string& query,
+      SnapshotType snapshot_type,
       int id,
       base::PersistentHistogramAllocator* allocator);
 
@@ -57,6 +71,12 @@ class SubprocessMetricsProvider : public metrics::MetricsProvider,
   void RecordHistogramSnapshots(
       base::HistogramSnapshotManager* snapshot_manager) override;
 
+  // base::StatisticsRecorder::MetricsDisplayer:
+  void WriteTitleString(std::string* output) override;
+  void WriteGraphs(const std::string& query,
+                   DisplayType format,
+                   std::string* output) override;
+
   // content::NotificationObserver:
   void Observe(int type,
                const content::NotificationSource& source,
@@ -69,14 +89,16 @@ class SubprocessMetricsProvider : public metrics::MetricsProvider,
                            int exit_code) override;
   void RenderProcessHostDestroyed(content::RenderProcessHost* host) override;
 
-  base::ThreadChecker thread_checker_;
+  // Lock for accessing objects. This is required because MetricsDisplayer is
+  // typically called by a background thread.
+  base::Lock lock_;
 
   // Object for registing notification requests.
   content::NotificationRegistrar registrar_;
 
   // All of the shared-persistent-allocators for known sub-processes.
   using AllocatorByIdMap =
-      IDMap<base::PersistentHistogramAllocator, IDMapOwnPointer, int>;
+      std::map<int, std::unique_ptr<base::PersistentHistogramAllocator>>;
   AllocatorByIdMap allocators_by_id_;
 
   // Allocators that are no longer attached to a subprocess, to be released