[iOS] Add a named guide for the BVC content area.

Adds a named guide to the content area so it can be positionally matched by transitions.

Cq-Include-Trybots: luci.chromium.try:ios-simulator-full-configs;master.tryserver.chromium.mac:ios-simulator-cronet
Change-Id: Ifcb0d873d88cf0af2b9f898a8d9e151b601504da
Reviewed-on: https://chromium-review.googlesource.com/1118169
Commit-Queue: Mark Cogan <marq@chromium.org>
Reviewed-by: Gauthier Ambard <gambard@chromium.org>
Cr-Commit-Position: refs/heads/master@{#571527}

ios/chrome/browser/ui/browser_view_controller.mm

@@ -1609,7 +1609,6 @@ applicationCommandEndpoint:(id<ApplicationCommands>)applicationCommandEndpoint {
 
 #pragma mark - UIViewController
 
-// Perform additional set up after loading the view, typically from a nib.
 - (void)viewDidLoad {
   CGRect initialViewsRect = self.view.bounds;
   if (!self.usesFullscreenContainer) {
@@ -2403,6 +2402,7 @@ applicationCommandEndpoint:(id<ApplicationCommands>)applicationCommandEndpoint {
            aboveSubview:self.primaryToolbarCoordinator.viewController.view];
     }
     NSArray<GuideName*>* guideNames = @[
+      kContentAreaGuide,
       kOmniboxGuide,
       kBackButtonGuide,
       kForwardButtonGuide,
@@ -2413,6 +2413,33 @@ applicationCommandEndpoint:(id<ApplicationCommands>)applicationCommandEndpoint {
       kVoiceSearchButtonGuide,
     ];
     AddNamedGuidesToView(guideNames, self.view);
+
+    // Configure the content area guide.
+    NamedGuide* contentAreaGuide =
+        [NamedGuide guideWithName:kContentAreaGuide view:self.view];
+
+    // Constrain top to bottom of top toolbar.
+    UIView* primaryToolbarView =
+        self.primaryToolbarCoordinator.viewController.view;
+    [contentAreaGuide.topAnchor
+        constraintEqualToAnchor:primaryToolbarView.bottomAnchor]
+        .active = YES;
+
+    LayoutSides contentSides = LayoutSides::kLeading | LayoutSides::kTrailing;
+    if (self.secondaryToolbarCoordinator) {
+      // If there's a bottom toolbar, the content area guide is constrained to
+      // its top.
+      UIView* secondaryToolbarView =
+          self.secondaryToolbarCoordinator.viewController.view;
+      [contentAreaGuide.bottomAnchor
+          constraintEqualToAnchor:secondaryToolbarView.topAnchor]
+          .active = YES;
+    } else {
+      // Otherwise, the content area guide is constrained to self.view's bootom
+      // along with its sides;
+      contentSides = contentSides | LayoutSides::kBottom;
+    }
+    AddSameConstraintsToSides(self.view, contentAreaGuide, contentSides);
   }
   if (initialLayout) {
     [self.primaryToolbarCoordinator.viewController

ios/chrome/browser/ui/util/layout_guide_names.h

@@ -12,6 +12,8 @@ typedef NSString GuideName;
 // The list of well-known UILayoutGuides.  When adding a new guide to the app,
 // create a constant for it below.
 
+// A guide that is constrained to match the frame of the tab's content area.
+extern GuideName* const kContentAreaGuide;
 // A guide that is constrained to match the frame of the secondary toolbar.
 extern GuideName* const kSecondaryToolbar;
 // A guide that is constrained to match the frame the secondary toolbar would

ios/chrome/browser/ui/util/layout_guide_names.mm

@@ -8,6 +8,7 @@
 #error "This file requires ARC support."
 #endif
 
+GuideName* const kContentAreaGuide = @"ContentAreaGuide";
 GuideName* const kSecondaryToolbar = @"kSecondaryToolbar";
 GuideName* const kSecondaryToolbarNoFullscreen =
     @"kSecondaryToolbarNoFullscreen";

ios/chrome/browser/ui/util/named_guide_util.h

@@ -7,7 +7,7 @@
 
 #import "ios/chrome/browser/ui/util/layout_guide_names.h"
 
-// Adds NamedGuides with the GuideNames in |names| to |view|.
+// Creates NamedGuides with the GuideNames in |names| and adds them to |view|.
 void AddNamedGuidesToView(NSArray<GuideName*>* names, UIView* view);
 
 // Sets the constrained views for the NamedGuides indicated by the keys of