Make SDCH dictionaries persistent across browser restart.

This CL also adds a generic persistence mechanism for //net, separate
from Chrome user preferences, that loads asynchronously on startup (i.e.
doesn't block startup).

This is a reupload of rdsmith@'s existing CL at
https://codereview.chromium.org/881413003/; see that CL for earlier discussion.

BUG=374915
R=mmenke@chromium.org
R=rdsmith@chromium.org
R=bauerb@chromium.org

Review URL: https://codereview.chromium.org/901303002

Cr-Commit-Position: refs/heads/master@{#319753}

1 files changed, 69 insertions, 7 deletions

diff --git a/net/sdch/sdch_owner.h b/net/sdch/sdch_owner.h
index e75c780..a187a6e 100644
--- a/net/sdch/sdch_owner.h
+++ b/net/sdch/sdch_owner.h
@@ -5,13 +5,19 @@
 #ifndef NET_SDCH_SDCH_OWNER_H_
 #define NET_SDCH_SDCH_OWNER_H_
 
+#include <map>
 #include <string>
 
 #include "base/memory/memory_pressure_listener.h"
+#include "base/memory/ref_counted.h"
+#include "base/prefs/pref_store.h"
 #include "net/base/sdch_observer.h"
 #include "net/url_request/sdch_dictionary_fetcher.h"
 
 class GURL;
+class PersistentPrefStore;
+class ValueMapPrefStore;
+class WriteablePrefStore;
 
 namespace base {
 class Clock;
@@ -25,7 +31,8 @@ class URLRequestContext;
 // exposes interface for setting SDCH policy.  It should be instantiated by
 // the net/ embedder.
 // TODO(rdsmith): Implement dictionary prioritization.
-class NET_EXPORT SdchOwner : public net::SdchObserver {
+class NET_EXPORT SdchOwner : public net::SdchObserver,
+                             public PrefStore::Observer {
  public:
   static const size_t kMaxTotalDictionarySize;
   static const size_t kMinSpaceForDictionaryFetch;
@@ -35,6 +42,13 @@ class NET_EXPORT SdchOwner : public net::SdchObserver {
   SdchOwner(net::SdchManager* sdch_manager, net::URLRequestContext* context);
   ~SdchOwner() override;
 
+  // Enables use of pref persistence.  Note that |pref_store| is owned
+  // by the caller, but must be guaranteed to outlive SdchOwner.  The
+  // actual mechanisms by which the PersistentPrefStore are persisted
+  // are the responsibility of the caller.  This routine may only be
+  // called once per SdchOwner instance.
+  void EnablePersistentStorage(PersistentPrefStore* pref_store);
+
   // Defaults to kMaxTotalDictionarySize.
   void SetMaxTotalDictionarySize(size_t max_total_dictionary_size);
 
@@ -49,18 +63,34 @@ class NET_EXPORT SdchOwner : public net::SdchObserver {
                        const GURL& dictionary_url) override;
   void OnClearDictionaries(net::SdchManager* manager) override;
 
-  // Implementation detail--this is the pathway through which the
-  // fetcher informs the SdchOwner that it's gotten the dictionary.
+  // PrefStore::Observer implementation.
+  void OnPrefValueChanged(const std::string& key) override;
+  void OnInitializationCompleted(bool succeeded) override;
+
+  // Implementation detail--this is the function callback by the callback
+  // passed to the fetcher through which the fetcher informs the SdchOwner
+  // that it's gotten the dictionary.  The first two arguments are
+  // bound locally.
   // Public for testing.
-  void OnDictionaryFetched(const std::string& dictionary_text,
+  void OnDictionaryFetched(base::Time last_used,
+                           int use_count,
+                           const std::string& dictionary_text,
                            const GURL& dictionary_url,
                            const net::BoundNetLog& net_log);
 
   void SetClockForTesting(scoped_ptr<base::Clock> clock);
 
+  // Returns the total number of dictionaries loaded.
+  int GetDictionaryCountForTesting() const;
+
+  // Returns whether this SdchOwner has dictionary from |url| loaded.
+  bool HasDictionaryFromURLForTesting(const GURL& url) const;
+
+  void SetFetcherForTesting(scoped_ptr<SdchDictionaryFetcher> fetcher);
+
  private:
   // For each active dictionary, stores local info.
-  // Indexed by server hash.
+  // Indexed by the server hash of the dictionary.
   struct DictionaryInfo {
     base::Time last_used;
     int use_count;
@@ -76,10 +106,18 @@ class NET_EXPORT SdchOwner : public net::SdchObserver {
   void OnMemoryPressure(
       base::MemoryPressureListener::MemoryPressureLevel level);
 
+  // Schedule loading of all dictionaries described in |persisted_info|.
+  // Returns false and does not schedule a load if |persisted_info| has an
+  // unsupported version or no dictionaries key. Skips any dictionaries that are
+  // malformed in |persisted_info|.
+  bool SchedulePersistedDictionaryLoads(
+      const base::DictionaryValue& persisted_info);
+
+  bool IsPersistingDictionaries() const;
+
   net::SdchManager* manager_;
-  net::SdchDictionaryFetcher fetcher_;
+  scoped_ptr<net::SdchDictionaryFetcher> fetcher_;
 
-  std::map<std::string, DictionaryInfo> local_dictionary_info_;
   size_t total_dictionary_bytes_;
 
   scoped_ptr<base::Clock> clock_;
@@ -95,6 +133,30 @@ class NET_EXPORT SdchOwner : public net::SdchObserver {
   // TODO(rmcilroy) Add back memory_pressure_listener_ when
   // http://crbug.com/447208 is fixed
 
+  // Dictionary persistence machinery.
+  // * |in_memory_pref_store_| is created on construction and used in
+  //   the absence of any call to EnablePersistentStorage().
+  // * |external_pref_store_| holds the preference store specified
+  //   by EnablePersistentStorage() (if any), while it is being read in.
+  //   A non-null value here signals that the SdchOwner is observing
+  //   the pref store; when read-in completes and observation is no longer
+  //   needed, the pointer is set to null.  This is to avoid lots of
+  //   extra irrelevant function calls; the only observer interface this
+  //   class is interested in is OnInitializationCompleted().
+  // * |pref_store_| holds an unowned pointer to the currently
+  //   active pref store (one of the preceding two).
+  scoped_refptr<ValueMapPrefStore> in_memory_pref_store_;
+  PersistentPrefStore* external_pref_store_;
+
+  WriteablePrefStore* pref_store_;
+
+  // The use counts of dictionaries when they were loaded from the persistent
+  // store, keyed by server hash. These are stored to avoid generating
+  // misleading ever-increasing use counts for dictionaries that are persisted,
+  // since the UMA histogram for use counts is only supposed to be since last
+  // load.
+  std::map<std::string, int> use_counts_at_load_;
+
   DISALLOW_COPY_AND_ASSIGN(SdchOwner);
 };