Revert to the old back arrow style with NavigationBar

MDC has a method to use the old style, but it's in a private component
and the wind is blowing towards removing it at some point, so this CL
just opt-s out of MDC driving the back button in Settings.

I still filed a request at MDC to have the method public, but it might
never come, or they might remove the old style before that.

BUG=none
R=sdefresne@chromium.org

Review-Url: https://codereview.chromium.org/2589193002
Cr-Commit-Position: refs/heads/master@{#439776}

ios/chrome/browser/ui/settings/autofill_settings_egtest.mm

@@ -145,7 +145,7 @@ void ClearCountryValue() {
 
 // Close the settings.
 - (void)exitSettingsMenu {
-  NSString* backButtonA11yId = @"back_bar_button";
+  NSString* backButtonA11yId = @"ic_arrow_back";
   [[EarlGrey
       selectElementWithMatcher:grey_allOf(
                                    grey_accessibilityID(backButtonA11yId),

ios/chrome/browser/ui/settings/block_popups_egtest.mm

@@ -81,13 +81,13 @@ void OpenBlockPopupsSettings() {
 void CloseSettings() {
   [[EarlGrey
       selectElementWithMatcher:grey_allOf(
-                                   grey_accessibilityID(@"back_bar_button"),
+                                   grey_accessibilityID(@"ic_arrow_back"),
                                    grey_accessibilityTrait(
                                        UIAccessibilityTraitButton),
                                    nil)] performAction:grey_tap()];
   [[EarlGrey
       selectElementWithMatcher:grey_allOf(
-                                   grey_accessibilityID(@"back_bar_button"),
+                                   grey_accessibilityID(@"ic_arrow_back"),
                                    grey_accessibilityTrait(
                                        UIAccessibilityTraitButton),
                                    nil)] performAction:grey_tap()];

ios/chrome/browser/ui/settings/settings_egtest.mm

@@ -273,11 +273,11 @@ bool IsCertificateCleared() {
       performAction:grey_tap()];
 }
 
-// Closes the a sub-settings menu, and then the general Settings menu.
+// Closes a sub-settings menu, and then the general Settings menu.
 - (void)closeSubSettingsMenu {
   [[EarlGrey
       selectElementWithMatcher:grey_allOf(
-                                   grey_accessibilityID(@"back_bar_button"),
+                                   grey_accessibilityID(@"ic_arrow_back"),
                                    grey_accessibilityTrait(
                                        UIAccessibilityTraitButton),
                                    nil)] performAction:grey_tap()];

ios/chrome/browser/ui/settings/settings_navigation_controller.mm

@@ -78,6 +78,11 @@
 // Closes the settings by calling |closeSettings| on |delegate|.
 - (void)closeSettings;
 
+// Creates an autoreleased Back button for a UINavigationItem which will pop the
+// top view controller when it is pressed. Should only be called by view
+// controllers owned by SettingsNavigationController.
+- (UIBarButtonItem*)backButton;
+
 // Creates an autoreleased "X" button that closes the settings when tapped.
 - (UIBarButtonItem*)closeButton;
 
@@ -319,6 +324,10 @@ initWithRootViewController:(UIViewController*)rootViewController
   [delegate_ closeSettings];
 }
 
+- (void)back {
+  [self popViewControllerAnimated:YES];
+}
+
 - (void)popViewControllerOrCloseSettingsAnimated:(BOOL)animated {
   if (self.viewControllers.count > 1) {
     // Pop the top view controller to reveal the view controller underneath.
@@ -351,6 +360,14 @@ initWithRootViewController:(UIViewController*)rootViewController
          [[rightButton title] compare:[doneButton title]] == NSOrderedSame;
 }
 
+- (UIBarButtonItem*)backButton {
+  // Create a custom Back bar button item, as Material Navigation Bar deprecated
+  // the back arrow with a shaft.
+  return [ChromeIcon templateBarButtonItemWithImage:[ChromeIcon backIcon]
+                                             target:self
+                                             action:@selector(back)];
+}
+
 - (UIBarButtonItem*)doneButton {
   // Create a custom Done bar button item, as Material Navigation Bar does not
   // handle a system UIBarButtonSystemItemDone item.
@@ -408,6 +425,12 @@ initWithRootViewController:(UIViewController*)rootViewController
 
 - (void)pushViewController:(UIViewController*)viewController
                   animated:(BOOL)animated {
+  // Add a back button if the view controller is not the root view controller
+  // and doesn’t already have a left bar button item.
+  if (self.viewControllers.count > 0 &&
+      viewController.navigationItem.leftBarButtonItems.count == 0) {
+    viewController.navigationItem.leftBarButtonItem = [self backButton];
+  }
   // Wrap the view controller in an MDCAppBarContainerViewController if needed.
   [super pushViewController:[self wrappedControllerIfNeeded:viewController]
                    animated:animated];

ios/chrome/browser/ui/settings/translate_ui_egtest.mm

@@ -58,13 +58,13 @@ const CGFloat kScrollDisplacement = 50.0;
   // Close settings.
   [[EarlGrey
       selectElementWithMatcher:grey_allOf(
-                                   grey_accessibilityID(@"back_bar_button"),
+                                   grey_accessibilityID(@"ic_arrow_back"),
                                    grey_accessibilityTrait(
                                        UIAccessibilityTraitButton),
                                    nil)] performAction:grey_tap()];
   [[EarlGrey
       selectElementWithMatcher:grey_allOf(
-                                   grey_accessibilityID(@"back_bar_button"),
+                                   grey_accessibilityID(@"ic_arrow_back"),
                                    grey_accessibilityTrait(
                                        UIAccessibilityTraitButton),
                                    nil)] performAction:grey_tap()];