Add a feature for limiting Safe Browsing database size on iOS

This adds a feature that limits the number of entries in
each Safe Browsing list to 2^{18}, which can be used to
measure the impact of limiting the size of the Safe
Browsing database.

Change-Id: Ieef0697ca60e6cd2c65e13b32b425a6ce08c0844
Bug: 1127429
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2402112
Commit-Queue: Ali Juma <ajuma@chromium.org>
Reviewed-by: Varun Khaneja <vakh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#806677}

components/safe_browsing/core/db/v4_update_protocol_manager.cc

@@ -13,6 +13,7 @@
 #include "base/metrics/histogram_macros.h"
 #include "base/rand_util.h"
 #include "base/timer/timer.h"
+#include "build/build_config.h"
 #include "components/safe_browsing/buildflags.h"
 #include "components/safe_browsing/core/db/safebrowsing.pb.h"
 #include "components/safe_browsing/core/features.h"
@@ -76,6 +77,12 @@ static const int kV4TimerStartIntervalSecMax = 300;
 // Maximum time, in seconds, to wait for a response to an update request.
 static const int kV4TimerUpdateWaitSecMax = 15 * 60;  // 15 minutes
 
+#if defined(OS_IOS)
+// Maximum number of entries in each list, when the limited list size experiment
+// is enabled.
+static const int kMaximumEntriesPerList = 1 << 18;
+#endif
+
 ChromeClientInfo::SafeBrowsingReportingPopulation GetReportingLevelProtoValue(
     ExtendedReportingLevel reporting_level) {
   switch (reporting_level) {
@@ -242,6 +249,13 @@ std::string V4UpdateProtocolManager::GetBase64SerializedUpdateRequestProto() {
     list_update_request->mutable_constraints()->add_supported_compressions(RAW);
     list_update_request->mutable_constraints()->add_supported_compressions(
         RICE);
+
+#if defined(OS_IOS)
+    if (base::FeatureList::IsEnabled(kLimitedListSizeForIOS)) {
+      list_update_request->mutable_constraints()->set_max_database_entries(
+          kMaximumEntriesPerList);
+    }
+#endif
   }
 
   if (!extended_reporting_level_callback_.is_null()) {

components/safe_browsing/core/features.cc

@@ -62,6 +62,9 @@ const base::Feature kEnhancedProtection {
 #endif
 };
 
+const base::Feature kLimitedListSizeForIOS{"SafeBrowsingLimitedListSizeForIOS",
+                                           base::FEATURE_DISABLED_BY_DEFAULT};
+
 const base::Feature kMalwareScanEnabled{"SafeBrowsingMalwareScanEnabled",
                                         base::FEATURE_DISABLED_BY_DEFAULT};
 
@@ -168,6 +171,7 @@ constexpr struct {
     {&kDelayedWarnings, true},
     {&kDownloadRequestWithToken, true},
     {&kEnhancedProtection, true},
+    {&kLimitedListSizeForIOS, true},
     {&kMalwareScanEnabled, true},
     {&kPasswordProtectionForSavedPasswords, true},
     {&kPasswordProtectionShowDomainsForSavedPasswords, true},

components/safe_browsing/core/features.h

@@ -49,6 +49,10 @@ extern const base::Feature kDownloadRequestWithToken;
 // Enable Chrome Safe Browsing enhanced protection.
 extern const base::Feature kEnhancedProtection;
 
+// Controls whether the limited list size experiment is enabled. This experiment
+// limits the number of entries stored in each Safe Browsing list.
+extern const base::Feature kLimitedListSizeForIOS;
+
 // Controls whether to do deep scanning for malware. If both this feature and
 // the enterprise policies are enabled, the downloaded and uploaded files are
 // sent for scanning.