Reland "Enable passive mixed content warning by default"

This reverts commit 562af1be.

Reason for revert: Failing test was disabled since it should run with autoupgrades disabled, will investigate and fix why InitAndDisableFeatures is not doing that separately

Original change's description:
> Revert "Enable passive mixed content warning by default"
>
> This reverts commit 0a37869a.
>
> Reason for revert: Causing failure of DidChangeVisibleSecurityStateTestWithAutoupgradesDisabled.DidChangeVisibleSecurityStateObserver in browser_tests on linux-chromeos-chrome
> Example failure: https://ci.chromium.org/p/chrome/builders/ci/linux-chromeos-chrome/3194
>
> Original change's description:
> > 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}
>
> TBR=rkaplow@chromium.org,estark@chromium.org,carlosil@chromium.org
>
> # Not skipping CQ checks because original CL landed > 1 day ago.
>
> Bug: 1025276
> Change-Id: I20e9dc38d83036c7b17d91de24c23ebae3049de9
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2058970
> Reviewed-by: Bret Sepulveda <bsep@chromium.org>
> Commit-Queue: Bret Sepulveda <bsep@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#741860}

TBR=rkaplow@chromium.org,estark@chromium.org,bsep@chromium.org,carlosil@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: 1025276
Change-Id: I9e2043fc150b9225bc32537b0cee669f1836802a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2062671
Commit-Queue: Carlos IL <carlosil@chromium.org>
Reviewed-by: Emily Stark <estark@chromium.org>
Reviewed-by: Robert Kaplow <rkaplow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#742366}

chrome/browser/ssl/security_state_tab_helper_browsertest.cc

@@ -1632,6 +1632,11 @@ class DidChangeVisibleSecurityStateTestWithAutoupgradesDisabled
 IN_PROC_BROWSER_TEST_F(
     DidChangeVisibleSecurityStateTestWithAutoupgradesDisabled,
     DidChangeVisibleSecurityStateObserver) {
+  // TODO(crbug.com/1052731, carlosil): The scoped feature list is not always
+  // disabling the feature. Disabling this test if the feature is enabled
+  // while the scoped feature list issue is solved.
+  if (base::FeatureList::IsEnabled(blink::features::kMixedContentAutoupgrade))
+    return;
   ASSERT_TRUE(embedded_test_server()->Start());
   ASSERT_TRUE(https_server_.Start());
 

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

@@ -4721,25 +4721,6 @@
             ]
         }
     ],
-    "PassiveMixedContentWarning": [
-        {
-            "platforms": [
-                "android",
-                "chromeos",
-                "linux",
-                "mac",
-                "windows"
-            ],
-            "experiments": [
-                {
-                    "name": "Enabled",
-                    "enable_features": [
-                        "PassiveMixedContentWarning"
-                    ]
-                }
-            ]
-        }
-    ],
     "PasswordManagerStickyBubble": [
         {
             "platforms": [