Fix IsPrecachingAllowed() to check Sync instead of Data Saver.

components/precache/content/precache_manager.cc

Index: components/precache/content/precache_manager.cc
diff --git a/components/precache/content/precache_manager.cc b/components/precache/content/precache_manager.cc
index 9e55564615f90746491a3eaa1e7ece6fb441f321..aca00a0b3ee2b2f1b53af00550cea5dabe3e6c8a 100644
--- a/components/precache/content/precache_manager.cc
+++ b/components/precache/content/precache_manager.cc
@@ -15,11 +15,10 @@
 #include "base/metrics/field_trial.h"
 #include "base/prefs/pref_service.h"
 #include "base/time/time.h"
-#include "components/data_reduction_proxy/core/common/data_reduction_proxy_pref_names.h"
 #include "components/history/core/browser/history_service.h"
 #include "components/precache/core/precache_database.h"
 #include "components/precache/core/precache_switches.h"
-#include "components/user_prefs/user_prefs.h"
+#include "components/sync_driver/sync_service.h"
 #include "components/variations/variations_associated_data.h"
 #include "content/public/browser/browser_context.h"
 #include "content/public/browser/browser_thread.h"
@@ -42,8 +41,10 @@ int NumTopHosts() {
   return kNumTopHosts;
 }
 
-PrecacheManager::PrecacheManager(content::BrowserContext* browser_context)
+PrecacheManager::PrecacheManager(content::BrowserContext* browser_context,
+                                 sync_driver::SyncService* sync_service)
     : browser_context_(browser_context),
+      sync_service_(sync_service),
       precache_database_(new PrecacheDatabase()),
       is_precaching_(false) {
   base::FilePath db_path(browser_context_->GetPath().Append(
@@ -66,9 +67,10 @@ bool PrecacheManager::IsPrecachingEnabled() {
 }
 
 bool PrecacheManager::IsPrecachingAllowed() {
-  DCHECK_CURRENTLY_ON(BrowserThread::UI);
-  return user_prefs::UserPrefs::Get(browser_context_)->GetBoolean(
-      data_reduction_proxy::prefs::kDataReductionProxyEnabled);
+  return sync_service_ && sync_service_->CanSyncStart() &&
+         sync_service_->HasSyncSetupCompleted() &&
+         sync_service_->GetPreferredDataTypes().Has(syncer::SESSIONS) &&
+         !sync_service_->GetEncryptedDataTypes().Has(syncer::SESSIONS);

[Nicolas Zea, 2015/06/18 18:25:48]

One correction (which I think was overlooked in the email):
GetEncryptedDataTypes will return the minimal set (just passwords) if sync's
backend hasn't initialized yet, and will also not take into account any pending
configuration changes (that haven't been finalized). Given the goal of this, I
think it's safer to ensure sync's backend is loaded and check
EncryptEverythingEnabled.

As such, the condition should be (instead of GetEncryptedDataTypes):
sync_service->backend_initialized() && !sync_service->EncryptEverythingEnabled()

It's yet uglier, but this is starting to dig into the internal of sync state,
which has to be concerned with transient issues. Really, the safest approach
would be the one that checks runtime conditions rather than preferences:
sync_service && sync_service->GetActiveDataTypes().Has(syncer::SESSIONS) &&
!sync_service->EncryptEverythingEnabled().

This does have the effect of meaning precaching would be disabled during the
time sync hasn't yet loaded or is shutting down, but from a privacy standpoint
I'm guessing that's okay?

 }
 
 void PrecacheManager::StartPrecaching(