[ios] Always show the swipe curtain with slim navigation enabled.

Bug: 820036
Cq-Include-Trybots: luci.chromium.try:ios-simulator-full-configs;master.tryserver.chromium.mac:ios-simulator-cronet
Change-Id: I3a7a713b90cfb314685b680cbf476d115a9c3771
Reviewed-on: https://chromium-review.googlesource.com/1101246
Commit-Queue: Justin Cohen <justincohen@chromium.org>
Reviewed-by: Eugene But <eugenebut@chromium.org>
Reviewed-by: Danyao Wang <danyao@chromium.org>
Cr-Commit-Position: refs/heads/master@{#567664}

ios/chrome/browser/ui/side_swipe/side_swipe_controller.mm

@@ -32,6 +32,7 @@
 #import "ios/chrome/browser/ui/toolbar/public/side_swipe_toolbar_interacting.h"
 #include "ios/chrome/browser/ui/ui_util.h"
 #import "ios/chrome/browser/web/page_placeholder_tab_helper.h"
+#import "ios/web/public/web_client.h"
 #import "ios/web/public/web_state/web_state_observer_bridge.h"
 
 #if !defined(__has_feature) || !__has_feature(objc_arc)
@@ -471,7 +472,13 @@ const NSUInteger kIpadGreySwipeTabCount = 8;
           [currentContentProvider_ goForward:webState];
         }
 
-        if (webState && webState->IsLoading()) {
+        // Checking -IsLoading() is likely incorrect, but to narrow the scope of
+        // fixes for slim navigation manager, only ignore this state when
+        // slim is disabled.  With slim navigation enabled, this false when
+        // pages can be served from WKWebView's page cache.
+        if (webState &&
+            (web::GetWebClient()->IsSlimNavigationManagerEnabled() ||
+             webState->IsLoading())) {
           scopedWebStateObserver_->RemoveAll();
           scopedWebStateObserver_->Add(webState);
           [self addCurtainWithCompletionHandler:^{
@@ -578,7 +585,20 @@ const NSUInteger kIpadGreySwipeTabCount = 8;
 
 #pragma mark - CRWWebStateObserver Methods
 
+// Checking -webStateDidStopLoading is likely incorrect, but to narrow the scope
+// of fixes for slim navigation manager, only ignore this callback when slim is
+// disabled.
 - (void)webStateDidStopLoading:(web::WebState*)webState {
+  if (web::GetWebClient()->IsSlimNavigationManagerEnabled())
+    return;
+  [self dismissCurtainWithCompletionHandler:^{
+    inSwipe_ = NO;
+  }];
+}
+
+- (void)webState:(web::WebState*)webState didLoadPageWithSuccess:(BOOL)success {
+  if (!web::GetWebClient()->IsSlimNavigationManagerEnabled())
+    return;
   [self dismissCurtainWithCompletionHandler:^{
     inSwipe_ = NO;
   }];