Add custom UIPresentationController for picker selector

ios/chrome/browser/ui/elements/selector_picker_presentation_controller.mm

Index: ios/chrome/browser/ui/elements/selector_picker_presentation_controller.mm
diff --git a/ios/chrome/browser/ui/elements/selector_picker_presentation_controller.mm b/ios/chrome/browser/ui/elements/selector_picker_presentation_controller.mm
new file mode 100644
index 0000000000000000000000000000000000000000..c7093131977ccdcd45573b3f1e4c6c1b81279efc
--- /dev/null
+++ b/ios/chrome/browser/ui/elements/selector_picker_presentation_controller.mm
@@ -0,0 +1,54 @@
+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#import "ios/chrome/browser/ui/elements/selector_picker_presentation_controller.h"
+
+#import "base/mac/objc_property_releaser.h"
+
+@interface SelectorPickerPresentationController () {
+  base::mac::ObjCPropertyReleaser
+      _propertyReleaser_SelectorPickerPresentationController;
+}
+@property(nonatomic, retain) UIView* dimmingView;
+@end
+
+@implementation SelectorPickerPresentationController
+
+@synthesize dimmingView = _dimmingView;
+
+- (instancetype)initWithPresentedViewController:(UIViewController*)presented
+                       presentingViewController:(UIViewController*)presenting {
+  self = [super initWithPresentedViewController:presented
+                       presentingViewController:presenting];
+  if (self) {
+    _propertyReleaser_SelectorPickerPresentationController.Init(
+        self, [SelectorPickerPresentationController class]);
+    _dimmingView = [[UIView alloc] initWithFrame:CGRectZero];
+    _dimmingView.backgroundColor = [UIColor colorWithWhite:0 alpha:0.4];
+  }
+  return self;
+}
+
+- (CGRect)frameOfPresentedViewInContainerView {
+  CGSize containerSize = self.containerView.frame.size;
+  CGSize pickerSize = [self.presentedView
+      systemLayoutSizeFittingSize:UILayoutFittingCompressedSize];
+  return CGRectMake(0, containerSize.height - pickerSize.height,
+                    containerSize.width, pickerSize.height);
+}
+
+- (void)containerViewWillLayoutSubviews {
+  self.dimmingView.frame = self.containerView.bounds;
+  self.presentedView.frame = [self frameOfPresentedViewInContainerView];
+}
+
+- (void)presentationTransitionWillBegin {
+  [self.containerView addSubview:self.dimmingView];
+}
+
+- (void)dismissalTransitionDidEnd:(BOOL)completed {
+  [self.dimmingView removeFromSuperview];
+}
+
+@end