Reland "[ios] Enable SlimNav and dependent features by default."

This reverts commit 063da117.

Reason for revert: Test disabled, relanding.

Original change's description:
> Revert "[ios] Enable SlimNav and dependent features by default."
> 
> This reverts commit 7c516511.
> 
> Reason for revert: <INSERT REASONING HERE>
> 
> Original change's description:
> > [ios] Enable SlimNav and dependent features by default.
> > 
> > Tentatively enabling this by default for M79.
> > 
> > Bug: 789582
> > Change-Id: I030902ddbb1a19f5b49a847b727c439cfd10fcf9
> > Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1787885
> > Reviewed-by: Rohit Rao <rohitrao@chromium.org>
> > Reviewed-by: Gauthier Ambard <gambard@chromium.org>
> > Reviewed-by: Eugene But <eugenebut@chromium.org>
> > Commit-Queue: Justin Cohen <justincohen@chromium.org>
> > Cr-Commit-Position: refs/heads/master@{#694620}
> 
> TBR=rohitrao@chromium.org,justincohen@chromium.org,eugenebut@chromium.org,gambard@chromium.org
> 
> Change-Id: Idb139bf5eed97036ccd2d0f26d331db77786b6e8
> No-Presubmit: true
> No-Tree-Checks: true
> No-Try: true
> Bug: 789582
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1789152
> Reviewed-by: Yi Su <mrsuyi@chromium.org>
> Commit-Queue: Yi Su <mrsuyi@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#694670}

TBR=rohitrao@chromium.org,justincohen@chromium.org,eugenebut@chromium.org,gambard@chromium.org,mrsuyi@chromium.org

Change-Id: Ia3470ee5f77a5171af99940b0efa32104cfdb873
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 789582, 1001965
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1791266Reviewed-by: Justin Cohen <justincohen@chromium.org>
Commit-Queue: Justin Cohen <justincohen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#694716}

ios/chrome/browser/metrics/features.cc

@@ -5,4 +5,4 @@
 #include "ios/chrome/browser/metrics/features.h"
 
 const base::Feature kLogLoadStartedInDidStartNavigation{
-    "LogLoadStartedInDidStartNavigation", base::FEATURE_DISABLED_BY_DEFAULT};
+    "LogLoadStartedInDidStartNavigation", base::FEATURE_ENABLED_BY_DEFAULT};

ios/chrome/browser/reading_list/features.cc

@@ -10,7 +10,7 @@
 namespace reading_list {
 
 const base::Feature kOfflineVersionWithoutNativeContent{
-    "OfflineVersionWithoutNativeContent", base::FEATURE_DISABLED_BY_DEFAULT};
+    "OfflineVersionWithoutNativeContent", base::FEATURE_ENABLED_BY_DEFAULT};
 
 bool IsOfflinePageWithoutNativeContentEnabled() {
   return base::FeatureList::IsEnabled(kOfflineVersionWithoutNativeContent) ||

ios/web/common/features.mm

@@ -15,7 +15,7 @@ const base::Feature kIgnoresViewportScaleLimits{
     "IgnoresViewportScaleLimits", base::FEATURE_ENABLED_BY_DEFAULT};
 
 const base::Feature kSlimNavigationManager{"SlimNavigationManager",
-                                           base::FEATURE_DISABLED_BY_DEFAULT};
+                                           base::FEATURE_ENABLED_BY_DEFAULT};
 
 const base::Feature kWKHTTPSystemCookieStore{"WKHTTPSystemCookieStore",
                                              base::FEATURE_ENABLED_BY_DEFAULT};