SQLitePersistentCookieStore: Attempt to diagnose occasional heavy memory consumption

From leak reports, it seems like sometimes the pending operations queue
just keeps growing and growing, but we still don't know why... so
DumpWithoutCrashing (once per backend lifetime) if it seems ridiculously
long.

Thanks to mef@ for the idea.

Bug: 809199
Change-Id: Ia949be30e50ddcd6f800c4c26268966b6e298bc0
Reviewed-on: https://chromium-review.googlesource.com/1210367
Commit-Queue: Maks Orlovich <morlovich@chromium.org>
Reviewed-by: Victor Costan <pwnall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#589236}

net/extras/sqlite/sqlite_persistent_cookie_store.cc

@@ -11,6 +11,8 @@
 
 #include "base/bind.h"
 #include "base/callback.h"
+#include "base/debug/alias.h"
+#include "base/debug/dump_without_crashing.h"
 #include "base/files/file_path.h"
 #include "base/files/file_util.h"
 #include "base/location.h"
@@ -181,6 +183,7 @@ class SQLitePersistentCookieStore::Backend
         initialized_(false),
         corruption_detected_(false),
         restore_old_session_cookies_(restore_old_session_cookies),
+        reported_giant_queue_(false),
         num_cookies_read_(0),
         client_task_runner_(client_task_runner),
         background_task_runner_(background_task_runner),
@@ -310,6 +313,9 @@ class SQLitePersistentCookieStore::Backend
   // Batch a cookie operation (add or delete)
   void BatchOperation(PendingOperation::OperationType op,
                       const CanonicalCookie& cc);
+
+  void ReportGiantQueue(size_t size);
+
   // Commit our pending operations to the database.
   void Commit();
   // Close() executed on the background runner.
@@ -357,6 +363,10 @@ class SQLitePersistentCookieStore::Backend
   // If false, we should filter out session cookies when reading the DB.
   bool restore_old_session_cookies_;
 
+  // If true, we already reported a failure due to seemingly wedged
+  // operations queue, so don't do it again.
+  bool reported_giant_queue_;
+
   // The cumulative time spent loading the cookies on the background runner.
   // Incremented and reported from the background runner.
   base::TimeDelta cookie_load_duration_;
@@ -1257,6 +1267,10 @@ void SQLitePersistentCookieStore::Backend::BatchOperation(
   static const int kCommitIntervalMs = 30 * 1000;
   // Commit right away if we have more than 512 outstanding operations.
   static const size_t kCommitAfterBatchSize = 512;
+
+  // Threshold after which we report a problem.
+  static const size_t kReportGiantQueueSizeThreshold = 50 * 1024;
+
   DCHECK(!background_task_runner_->RunsTasksInCurrentSequence());
 
   // We do a full copy of the cookie here, and hopefully just here.
@@ -1279,9 +1293,19 @@ void SQLitePersistentCookieStore::Backend::BatchOperation(
   } else if (num_pending == kCommitAfterBatchSize) {
     // We've reached a big enough batch, fire off a commit now.
     PostBackgroundTask(FROM_HERE, base::Bind(&Backend::Commit, this));
+  } else if (num_pending >= kReportGiantQueueSizeThreshold &&
+             !reported_giant_queue_) {
+    ReportGiantQueue(num_pending);
+    reported_giant_queue_ = true;
   }
 }
 
+void SQLitePersistentCookieStore::Backend::ReportGiantQueue(
+    size_t num_pending) {
+  base::debug::Alias(&num_pending);
+  base::debug::DumpWithoutCrashing();
+}
+
 void SQLitePersistentCookieStore::Backend::Commit() {
   DCHECK(background_task_runner_->RunsTasksInCurrentSequence());