PVer4: Add UMA metrics for time taken to: load DB, do prefix check,

components/safe_browsing_db/v4_database.cc

Index: components/safe_browsing_db/v4_database.cc
diff --git a/components/safe_browsing_db/v4_database.cc b/components/safe_browsing_db/v4_database.cc
index 4b43498c5abf4bd2139d42ca51ef8528738694ef..b0580304b8009e15ad2bc13c74270ee2e20d442d 100644
--- a/components/safe_browsing_db/v4_database.cc
+++ b/components/safe_browsing_db/v4_database.cc
@@ -8,11 +8,13 @@
 #include "base/debug/leak_annotations.h"
 #include "base/files/file_util.h"
 #include "base/memory/ptr_util.h"
+#include "base/metrics/histogram_macros.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "components/safe_browsing_db/v4_database.h"
 #include "content/public/browser/browser_thread.h"
 
 using content::BrowserThread;
+using base::TimeTicks;
 
 namespace safe_browsing {
 
@@ -31,9 +33,9 @@ void V4Database::Create(
   const scoped_refptr<base::SingleThreadTaskRunner> callback_task_runner =
       base::ThreadTaskRunnerHandle::Get();
   db_task_runner->PostTask(
-      FROM_HERE,
-      base::Bind(&V4Database::CreateOnTaskRunner, db_task_runner, base_path,
-                 list_infos, callback_task_runner, new_db_callback));
+      FROM_HERE, base::Bind(&V4Database::CreateOnTaskRunner, db_task_runner,
+                            base_path, list_infos, callback_task_runner,
+                            new_db_callback, TimeTicks::Now()));
 }
 
 // static
@@ -42,7 +44,8 @@ void V4Database::CreateOnTaskRunner(
     const base::FilePath& base_path,
     const ListInfos& list_infos,
     const scoped_refptr<base::SingleThreadTaskRunner>& callback_task_runner,
-    NewDatabaseReadyCallback new_db_callback) {
+    NewDatabaseReadyCallback new_db_callback,
+    const TimeTicks before) {
   DCHECK(db_task_runner->RunsTasksOnCurrentThread());
 
   if (!factory_) {
@@ -72,6 +75,10 @@ void V4Database::CreateOnTaskRunner(
   // thread. This would unblock resource loads.
   callback_task_runner->PostTask(
       FROM_HERE, base::Bind(new_db_callback, base::Passed(&v4_database)));
+
+  // TODO(vakh): Consider changing the following histogram name to be
+  // SafeBrowsing.V4DatabaseOpen.Time once PVer3 code is removed.
+  UMA_HISTOGRAM_TIMES("SB2.DatabaseOpen", TimeTicks::Now() - before);

[Nathan Parker, 2016/10/21 20:21:18]

note: This time includes the time to post onto this runner, but not back onto
the IO thread. That's probably fine (the second post might take few ms), but
let's make sure it's apples-to-apples with Pver3.

In the Hybrid experiment group, Chrome will log to this metric twice, once  for
v3 and once for v4. That will make this metric useless in that group since the
two distributions will be mashed together.  Sooo..  Maybe it makes sense to log
this to your new suggested metric for now. It'll mean it'll be a bit harder to
compare the two come v4only mode, but it's at least possible.

[vakh (use Gerrit instead), 2016/10/21 22:54:04]

PVer3 has the same.
Done.

 }
 
 V4Database::V4Database(