Enable passive mixed content warning by default

Sets the feature to enabled by default and removes the config from
fieldtrial_testing_config.json in preparation for launch.

Bug: 1025276
Change-Id: Iffcdd2153491de25b7038a609776255bbdacf2ac
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2053024
Commit-Queue: Carlos IL <carlosil@chromium.org>
Reviewed-by: Robert Kaplow <rkaplow@chromium.org>
Reviewed-by: Emily Stark <estark@chromium.org>
Auto-Submit: Carlos IL <carlosil@chromium.org>
Cr-Commit-Position: refs/heads/master@{#741506}

components/security_state/core/features.cc

@@ -22,7 +22,7 @@ const base::Feature kSafetyTipUI{"SafetyTip",
                                  base::FEATURE_DISABLED_BY_DEFAULT};
 
 const base::Feature kPassiveMixedContentWarning{
-    "PassiveMixedContentWarning", base::FEATURE_DISABLED_BY_DEFAULT};
+    "PassiveMixedContentWarning", base::FEATURE_ENABLED_BY_DEFAULT};
 
 }  // namespace features
 }  // namespace security_state

components/security_state/core/security_state_unittest.cc

@@ -303,7 +303,11 @@ TEST(SecurityStateTest, MixedContentWithPolicyCertificate) {
   // Verify that passive mixed content downgrades the security level.
   helper.set_contained_mixed_form(false);
   helper.set_displayed_mixed_content(true);
-  EXPECT_EQ(NONE, helper.GetSecurityLevel());
+  SecurityLevel expected_passive_level =
+      base::FeatureList::IsEnabled(features::kPassiveMixedContentWarning)
+          ? WARNING
+          : NONE;
+  EXPECT_EQ(expected_passive_level, helper.GetSecurityLevel());
 
   // Ensure that active mixed content downgrades the security level.
   helper.set_contained_mixed_form(false);

testing/variations/fieldtrial_testing_config.json

@@ -4673,25 +4673,6 @@
             ]
         }
     ],
-    "PassiveMixedContentWarning": [
-        {
-            "platforms": [
-                "android",
-                "chromeos",
-                "linux",
-                "mac",
-                "windows"
-            ],
-            "experiments": [
-                {
-                    "name": "Enabled",
-                    "enable_features": [
-                        "PassiveMixedContentWarning"
-                    ]
-                }
-            ]
-        }
-    ],
     "PasswordManagerStickyBubble": [
         {
             "platforms": [