[Password Manager] Add experiment controlling sync credential saving behavior

I also updated ProvisionalSaveFailure in histograms.xml, which was an oversight from a previous cl.

BUG=386402

Review URL: https://codereview.chromium.org/421563003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@288162 0039d316-1c4b-4281-b951-d872f2087c98

chrome/app/generated_resources.grd

@@ -6192,6 +6192,12 @@ Keep your key file in a safe place. You will need it to create new versions of y
       <message name="IDS_FLAGS_DEBUG_PACKED_APP_DESCRIPTION" desc="Description of the flag to enable debugging context menu options for packed apps.">
         Enables debugging context menu options such as Inspect Element for packed applications.
       </message>
+      <message name="IDS_FLAGS_ENABLE_DROP_SYNC_CREDENTIAL_NAME" desc="Name of the flag to enable drop sync credential">
+        Drop sync credentials from password manager.
+      </message>
+      <message name="IDS_FLAGS_ENABLE_DROP_SYNC_CREDENTIAL_DESCRIPTION" desc="Description of the flag to enable drop sync credential">
+        If enabled, the password manager will not offer to save the credential used to sync.
+      </message>
       <message name="IDS_FLAGS_ENABLE_PASSWORD_GENERATION_NAME" desc="Name of the flag to enable password generation.">
         Enable password generation.
       </message>

chrome/browser/about_flags.cc

@@ -499,6 +499,14 @@ const Experiment::Choice kRememberCertificateErrorDecisionsChoices[] = {
     "7776000" },
 };
 
+const Experiment::Choice kEnableDropSyncCredentialChoices[] = {
+  { IDS_GENERIC_EXPERIMENT_CHOICE_DEFAULT, "", ""},
+  { IDS_GENERIC_EXPERIMENT_CHOICE_ENABLED,
+    password_manager::switches::kEnableDropSyncCredential, "" },
+  { IDS_GENERIC_EXPERIMENT_CHOICE_DISABLED,
+    password_manager::switches::kDisableDropSyncCredential, "" },
+};
+
 // RECORDING USER METRICS FOR FLAGS:
 // -----------------------------------------------------------------------------
 // The first line of the experiment is the internal name. If you'd like to
@@ -1924,6 +1932,13 @@ const Experiment kExperiments[] = {
     kOsAll,
     MULTI_VALUE_TYPE(kRememberCertificateErrorDecisionsChoices)
   },
+  {
+    "enable-drop-sync-credential",
+    IDS_FLAGS_ENABLE_DROP_SYNC_CREDENTIAL_NAME,
+    IDS_FLAGS_ENABLE_DROP_SYNC_CREDENTIAL_DESCRIPTION,
+    kOsAll,
+    MULTI_VALUE_TYPE(kEnableDropSyncCredentialChoices)
+  }
 };
 
 const Experiment* experiments = kExperiments;

components/password_manager/core/browser/password_manager.cc

@@ -19,6 +19,7 @@
 #include "components/password_manager/core/browser/password_manager_driver.h"
 #include "components/password_manager/core/browser/password_manager_metrics_util.h"
 #include "components/password_manager/core/common/password_manager_pref_names.h"
+#include "components/password_manager/core/common/password_manager_switches.h"
 #include "components/pref_registry/pref_registry_syncable.h"
 
 using autofill::PasswordForm;
@@ -53,6 +54,21 @@ void ReportMetrics(bool password_manager_enabled) {
   UMA_HISTOGRAM_BOOLEAN("PasswordManager.Enabled", password_manager_enabled);
 }
 
+bool ShouldDropSyncCredential() {
+  std::string group_name =
+      base::FieldTrialList::FindFullName("PasswordManagerDropSyncCredential");
+
+  CommandLine* command_line = CommandLine::ForCurrentProcess();
+  if (command_line->HasSwitch(switches::kEnableDropSyncCredential))
+    return true;
+
+  if (command_line->HasSwitch(switches::kDisableDropSyncCredential))
+    return false;
+
+  // Default to not saving.
+  return group_name != "Disabled";
+}
+
 }  // namespace
 
 const char PasswordManager::kOtherPossibleUsernamesExperiment[] =
@@ -218,7 +234,8 @@ void PasswordManager::ProvisionallySavePassword(const PasswordForm& form) {
 
   // Don't save credentials for the syncing account. See crbug.com/365832 for
   // background.
-  if (client_->IsSyncAccountCredential(
+  if (ShouldDropSyncCredential() &&
+      client_->IsSyncAccountCredential(
           base::UTF16ToUTF8(form.username_value), form.signon_realm)) {
     RecordFailure(SYNC_CREDENTIAL, form.origin.host(), logger.get());
     return;

components/password_manager/core/common/password_manager_switches.cc

@@ -8,10 +8,18 @@ namespace password_manager {
 
 namespace switches {
 
+// Disable dropping the credential used to sync passwords.
+const char kDisableDropSyncCredential[] =
+    "disable-drop-sync-credential";
+
 // Disable both saving and filling for the sync signin form.
 const char kDisableManagerForSyncSignin[] =
     "disable-manager-for-sync-signin";
 
+// Enable dropping the credential used to sync passwords.
+const char kEnableDropSyncCredential[] =
+    "enable-drop-sync-credential";
+
 // Enable saving and filling for the sync signin form. Currently the default
 // behavior.
 const char kEnableManagerForSyncSignin[] =

components/password_manager/core/common/password_manager_switches.h

@@ -12,7 +12,9 @@ namespace switches {
 // All switches in alphabetical order. The switches should be documented
 // alongside the definition of their values in the .cc file.
 
+extern const char kDisableDropSyncCredential[];
 extern const char kDisableManagerForSyncSignin[];
+extern const char kEnableDropSyncCredential[];
 extern const char kEnableManagerForSyncSignin[];
 extern const char kEnableAutomaticPasswordSaving[];
 

tools/metrics/histograms/histograms.xml

@@ -46625,6 +46625,7 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   <int value="4" label="FORM_BLACKLISTED"/>
   <int value="5" label="INVALID_FORM"/>
   <int value="6" label="AUTOCOMPLETE_OFF"/>
+  <int value="7" label="SYNC_CREDENTIALS"/>
 </enum>
 
 <enum name="ProxyStatus" type="int">