Handle classes/externs that are not available on iOS 10.0

UI*FeedbackGenerator and AVCaptureDevice* classes are claimed to be
available for iOS 10+, but they are not really available at runtime on
iOS 10.0. iOS 10.1+ appears to be OK. Use workarounds for unavailable
symbols.

Bug: 824941
Cq-Include-Trybots: master.tryserver.chromium.mac:ios-simulator-cronet;master.tryserver.chromium.mac:ios-simulator-full-configs
Change-Id: Idb9e42e6f72cbd96ff81e99f3ec455c03e09f8ce
Reviewed-on: https://chromium-review.googlesource.com/976945
Commit-Queue: Peter Lee <pkl@chromium.org>
Reviewed-by: Eugene But <eugenebut@chromium.org>
Cr-Commit-Position: refs/heads/master@{#546240}

ios/chrome/browser/ui/qr_scanner/BUILD.gn

@@ -52,6 +52,19 @@ source_set("coordinator") {
   ]
 }
 
+source_set("unit_tests") {
+  configs += [ "//build/config/compiler:enable_arc" ]
+  testonly = true
+  sources = [
+    "camera_controller_unittest.mm",
+  ]
+  deps = [
+    ":qr_scanner",
+    "//base",
+    "//testing/gtest:gtest",
+  ]
+}
+
 source_set("eg_tests") {
   configs += [ "//build/config/compiler:enable_arc" ]
   testonly = true

ios/chrome/browser/ui/qr_scanner/camera_controller.mm

@@ -183,15 +183,28 @@
     // Get the back camera.
     NSArray* videoCaptureDevices = nil;
     if (@available(iOS 10, *)) {
+      // Although Apple documentation claims that
+      // AVCaptureDeviceDiscoverySession etc. is available on iOS 10+, they are
+      // not really available on an app whose deployment target is iOS 10.0
+      // (iOS 10.1+ are okay) and Chrome will fail at dynamic link time and
+      // instantly crash.  NSClassFromString() checks if Objective-C run-time
+      // has the classes before using them.
+      Class discoverSessionClass =
+          NSClassFromString(@"AVCaptureDeviceDiscoverySession");
+      if (discoverSessionClass) {
+        // Hardcoded value of AVCaptureDeviceTypeBuiltInWideAngleCamera here.
+        // When this @available(iOS 10, *) is deprecated, the unit test
+        // CameraControllerTest.TestAVCaptureDeviceValue can be removed.
+        // See https://crbug.com/826011
+        NSString* cameraType = @"AVCaptureDeviceTypeBuiltInWideAngleCamera";
         AVCaptureDeviceDiscoverySession* discoverySession =
-          [AVCaptureDeviceDiscoverySession
-              discoverySessionWithDeviceTypes:@[
-                AVCaptureDeviceTypeBuiltInWideAngleCamera
-              ]
+            [discoverSessionClass
+                discoverySessionWithDeviceTypes:@[ cameraType ]
                                       mediaType:AVMediaTypeVideo
                                        position:AVCaptureDevicePositionBack];
         videoCaptureDevices = [discoverySession devices];
       }
+    }
 #if !defined(__IPHONE_10_0) || __IPHONE_OS_VERSION_MIN_REQUIRED < __IPHONE_10_0
     else {
       videoCaptureDevices =

ios/chrome/browser/ui/qr_scanner/camera_controller_unittest.mm

+// Copyright 2018 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/qr_scanner/camera_controller.h"
+
+#include "testing/gtest_mac.h"
+#include "testing/platform_test.h"
+
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
+using CameraControllerTest = PlatformTest;
+
+TEST_F(CameraControllerTest, TestAVCaptureDeviceValue) {
+  // Although Apple documentation claims that AVCaptureDeviceDiscoverySession
+  // etc. is available on iOS 10+, they are not really available on an app
+  // whose deployment target is iOS 10.0 (iOS 10.1+ are okay) and Chrome will
+  // fail at dynamic link time and instantly crash. To make this work, the
+  // actual value for the global variable
+  // |AVCaptureDeviceTypeBuiltInWideAngleCamera| is used literally in
+  // camera_controller.mm. This unit test detects if a newer iOS version
+  // changes this value. If this unit test fails, check the implementation
+  // of -loadCaptureSession: in camera_controller.mm.
+  //
+  // The following use of AVCaptureDeviceTypeBuiltInWideAngleCamera
+  // will cause unit tests to be not runnable on iOS 10.0 devices due to
+  // failure at dynamic link (dyld) time.
+  // TODO(crbug.com/826011): Remove this when iOS 10.0 support is deprecated.
+  EXPECT_NSEQ(AVCaptureDeviceTypeBuiltInWideAngleCamera,
+              @"AVCaptureDeviceTypeBuiltInWideAngleCamera");
+}

ios/chrome/browser/ui/uikit_ui_util.mm

@@ -581,30 +581,56 @@ UIResponder* GetFirstResponder() {
 // action. This is a no-op for devices that do not support it.
 void TriggerHapticFeedbackForAction() {
   if (@available(iOS 10, *)) {
-    UIImpactFeedbackGenerator* generator =
-        [[UIImpactFeedbackGenerator alloc] init];
+    // Although Apple documentation claims that UIFeedbackGenerator and its
+    // concrete subclasses are available on iOS 10+, they are not really
+    // available on an app whose deployment target is iOS 10.0 (iOS 10.1+ are
+    // okay) and Chrome will fail at dynamic link time and instantly crash.
+    // NSClassFromString() checks if Objective-C run-time has the class before
+    // using it.
+    Class generatorClass = NSClassFromString(@"UIImpactFeedbackGenerator");
+    if (generatorClass) {
+      UIImpactFeedbackGenerator* generator = [[generatorClass alloc] init];
       [generator impactOccurred];
     }
+  }
 }
 
 // On iOS10 and above, trigger a haptic vibration for the change in selection.
 // This is a no-op for devices that do not support it.
 void TriggerHapticFeedbackForSelectionChange() {
   if (@available(iOS 10, *)) {
-    UISelectionFeedbackGenerator* generator =
-        [[UISelectionFeedbackGenerator alloc] init];
+    // Although Apple documentation claims that UIFeedbackGenerator and its
+    // concrete subclasses are available on iOS 10+, they are not really
+    // available on an app whose deployment target is iOS 10.0 (iOS 10.1+ are
+    // okay) and Chrome will fail at dynamic link time and instantly crash.
+    // NSClassFromString() checks if Objective-C run-time has the class before
+    // using it.
+    Class generatorClass = NSClassFromString(@"UISelectionFeedbackGenerator");
+    if (generatorClass) {
+      UISelectionFeedbackGenerator* generator = [[generatorClass alloc] init];
       [generator selectionChanged];
     }
+  }
 }
 
 // On iOS10 and above, trigger a haptic vibration for a notification.
 // This is a no-op for devices that do not support it.
 void TriggerHapticFeedbackForNotification(UINotificationFeedbackType type) {
   if (@available(iOS 10, *)) {
+    // Although Apple documentation claims that UIFeedbackGenerator and its
+    // concrete subclasses are available on iOS 10+, they are not really
+    // available on an app whose deployment target is iOS 10.0 (iOS 10.1+ are
+    // okay) and Chrome will fail at dynamic link time and instantly crash.
+    // NSClassFromString() checks if Objective-C run-time has the class before
+    // using it.
+    Class generatorClass =
+        NSClassFromString(@"UINotificationFeedbackGenerator");
+    if (generatorClass) {
       UINotificationFeedbackGenerator* generator =
-        [[UINotificationFeedbackGenerator alloc] init];
+          [[generatorClass alloc] init];
       [generator notificationOccurred:type];
     }
+  }
 }
 
 UIEdgeInsets SafeAreaInsetsForView(UIView* view) {

ios/chrome/test/BUILD.gn

@@ -213,6 +213,7 @@ test("ios_chrome_unittests") {
     "//ios/chrome/browser/ui/popup_menu:unit_tests",
     "//ios/chrome/browser/ui/presenters:unit_tests",
     "//ios/chrome/browser/ui/promos:unit_tests",
+    "//ios/chrome/browser/ui/qr_scanner:unit_tests",
     "//ios/chrome/browser/ui/reading_list:unit_tests",
     "//ios/chrome/browser/ui/safe_mode:unit_tests",
     "//ios/chrome/browser/ui/settings:unit_tests",