Use persistent memory for receiving metrics from sub-processes.

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 953169c8d8d34002de98100814c65f4c2df03d69..127eafe8872e8135194795055d4af8803ff149d5 100644
--- a/chrome/browser/metrics/subprocess_metrics_provider.h
+++ b/chrome/browser/metrics/subprocess_metrics_provider.h
@@ -10,9 +10,11 @@
 
 #include "base/gtest_prod_util.h"
 #include "base/id_map.h"
+#include "base/memory/weak_ptr.h"
 #include "base/scoped_observer.h"
 #include "base/threading/thread_checker.h"
 #include "components/metrics/metrics_provider.h"
+#include "content/public/browser/browser_child_process_observer.h"
 #include "content/public/browser/notification_observer.h"
 #include "content/public/browser/notification_registrar.h"
 #include "content/public/browser/render_process_host_observer.h"
@@ -27,12 +29,18 @@ class SharedPersistentMemoryAllocator;
 // when metrics are being collected for upload, or when something else needs
 // combined metrics (such as the chrome://histograms page).
 class SubprocessMetricsProvider : public metrics::MetricsProvider,
+                                  public content::BrowserChildProcessObserver,
                                   public content::NotificationObserver,
                                   public content::RenderProcessHostObserver {
  public:
   SubprocessMetricsProvider();
   ~SubprocessMetricsProvider() override;
 
+  // Start tracking sub-processes. This is called separately rather than being
+  // set in the constructor because library code that checks for calling on
+  // the correct thread can break tests.

[Alexei Svitkine (slow), 2016/08/12 23:14:36]

Can you provide more context? I would hope we can mock the current thread in
tests so that we don't need to do this, but I might be missing something.

[bcwhite, 2016/08/15 19:43:10]

There's a DCHECK that it's running on BrowserThread::UI which is not true for
tests.

Unless there's a way for a test to so designate its thread?

[Alexei Svitkine (slow), 2016/08/18 07:21:19]

See:
https://groups.google.com/a/chromium.org/forum/#!topic/chromium-dev/qQiWjlxRcE4

[Alexei Svitkine (slow), 2016/08/19 15:10:51]

Ping on this. I think you should be able to use the techniques mention in this
thread to avoid the separate function here.

[bcwhite, 2016/08/19 15:55:21]

Yep.  Was just addressing the design issues quickly before investigating.

Done.

+  void EnableSubprocessTracking();
+
  private:
   friend class SubprocessMetricsProviderTest;
 
@@ -56,6 +64,18 @@ class SubprocessMetricsProvider : public metrics::MetricsProvider,
   // metrics::MetricsProvider:
   void MergeHistogramDeltas() override;
 
+  // content::BrowserChildProcessObserver:
+  void BrowserChildProcessHostConnected(
+      const content::ChildProcessData& data) override;
+  void BrowserChildProcessHostDisconnected(
+      const content::ChildProcessData& data) override;
+  void BrowserChildProcessCrashed(
+      const content::ChildProcessData& data,
+      int exit_code) override;
+  void BrowserChildProcessKilled(
+      const content::ChildProcessData& data,
+      int exit_code) override;
+
   // content::NotificationObserver:
   void Observe(int type,
                const content::NotificationSource& source,
@@ -68,6 +88,13 @@ class SubprocessMetricsProvider : public metrics::MetricsProvider,
                            int exit_code) override;
   void RenderProcessHostDestroyed(content::RenderProcessHost* host) override;
 
+  // Indicates a browser child process to be monitored. This must be called on
+  // the IO thread. The |provider| is used for calling Register on the UI
+  // thread.
+  static void RegisterBrowserChildProcessAllocatorFromIOThread(
+      base::WeakPtr<SubprocessMetricsProvider> provider,
+      int id);
+
   base::ThreadChecker thread_checker_;
 
   // Object for registing notification requests.
@@ -82,6 +109,8 @@ class SubprocessMetricsProvider : public metrics::MetricsProvider,
   ScopedObserver<content::RenderProcessHost, SubprocessMetricsProvider>
       scoped_observer_;
 
+  base::WeakPtrFactory<SubprocessMetricsProvider> weak_ptr_factory_;
+
   DISALLOW_COPY_AND_ASSIGN(SubprocessMetricsProvider);
 };