Disable precache if data_reduction_proxy enabled.

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 f4333c12d64e9b02779ca6a8de304a99f2e8bcf5..5f12188fc413a7b5dde9a662d3bf037d870e4350 100644
--- a/components/precache/content/precache_manager.cc
+++ b/components/precache/content/precache_manager.cc
@@ -14,6 +14,7 @@
 #include "base/metrics/field_trial.h"
 #include "base/strings/string_util.h"
 #include "base/time/time.h"
+#include "components/data_reduction_proxy/core/browser/data_reduction_proxy_settings.h"
 #include "components/history/core/browser/history_service.h"
 #include "components/precache/core/precache_database.h"
 #include "components/precache/core/precache_switches.h"
@@ -36,6 +37,7 @@ const char kPrecacheFieldTrialEnabledGroup[] = "Enabled";
 const char kPrecacheFieldTrialControlGroup[] = "Control";
 const char kConfigURLParam[] = "config_url";
 const char kManifestURLPrefixParam[] = "manifest_url_prefix";
+const char kDataReductionProxyParam[] = "disable_if_data_reduction_proxy";
 const size_t kNumTopHosts = 100;
 
 }  // namespace
@@ -50,11 +52,14 @@ PrecacheManager::PrecacheManager(
     content::BrowserContext* browser_context,
     const syncer::SyncService* const sync_service,
     const history::HistoryService* const history_service,
+    const data_reduction_proxy::DataReductionProxySettings*
+        data_reduction_proxy_settings,
     const base::FilePath& db_path,
     std::unique_ptr<PrecacheDatabase> precache_database)
     : browser_context_(browser_context),
       sync_service_(sync_service),
       history_service_(history_service),
+      data_reduction_proxy_settings_(data_reduction_proxy_settings),
       is_precaching_(false) {
   precache_database_ = std::move(precache_database);
   BrowserThread::PostTask(
@@ -99,6 +104,13 @@ bool PrecacheManager::IsPrecachingAllowed() const {
 }
 
 PrecacheManager::AllowedType PrecacheManager::PrecachingAllowed() const {
+  bool disable_if_proxy = !variations::GetVariationParamValue(
+      kPrecacheFieldTrialName, kDataReductionProxyParam).empty();
+  if (disable_if_proxy &&
+      (!data_reduction_proxy_settings_ ||

[bengr, 2016/12/07 00:18:25]

You want to disable if you don't have a settings object? I would have thought
the condition would be:

(data_reduction_proxy_settings_ &&
!data_reduction_proxy_settings->IsDataReductionProxyEnabled())

[twifkak, 2016/12/07 02:13:35]

I believe the answer to your question is "Yes", but let me ask you, since you
know more about data_reduction_proxy than me.

When does DataReductionProxyChromeSettingsFactory::GetForBrowserContext() return
nullptr? My assumption was one of:

- The user visits a page in cognito. ChromeNetworkDelegate calls
precache::UpdatePrecacheMetricsAndState (in order to maybe record UMAs).
- Something horrible has happened.

In both cases, I'd want to act conservatively and disable.

There's a third possible scenario:
- Native libs just loaded and browser is setting up.

But I just tested this scenario and it doesn't seem to a problem.

+       data_reduction_proxy_settings_->IsDataReductionProxyEnabled()))
+    return AllowedType::DISALLOWED;
+
   if (!(sync_service_ && sync_service_->IsBackendInitialized()))
     return AllowedType::PENDING;