Update iOS AppRTCDemo to use level controller.

webrtc/sdk/objc/Framework/Classes/RTCMediaConstraints.mm

 /*
  *  Copyright 2015 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 12 matching lines @@
 NSString * const kRTCMediaConstraintsMaxWidth =
     @(webrtc::MediaConstraintsInterface::kMaxWidth);
 NSString * const kRTCMediaConstraintsMinHeight =
     @(webrtc::MediaConstraintsInterface::kMinHeight);
 NSString * const kRTCMediaConstraintsMaxHeight =
     @(webrtc::MediaConstraintsInterface::kMaxHeight);
 NSString * const kRTCMediaConstraintsMinFrameRate =
     @(webrtc::MediaConstraintsInterface::kMinFrameRate);
 NSString * const kRTCMediaConstraintsMaxFrameRate =
     @(webrtc::MediaConstraintsInterface::kMaxFrameRate);
+NSString * const kRTCMediaConstraintsLevelControl =
+    @(webrtc::MediaConstraintsInterface::kLevelControl);
+
+NSString * const kRTCMediaConstraintsValueTrue =
+    @(webrtc::MediaConstraintsInterface::kValueTrue);
+NSString * const kRTCMediaConstraintsValueFalse =
+    @(webrtc::MediaConstraintsInterface::kValueFalse);
 
 namespace webrtc {
 
 MediaConstraints::~MediaConstraints() {}
 
 MediaConstraints::MediaConstraints() {}
 
 MediaConstraints::MediaConstraints(
     const MediaConstraintsInterface::Constraints& mandatory,
     const MediaConstraintsInterface::Constraints& optional)
@@ skipping 59 matching lines @@
     NSString *value = [constraints objectForKey:key];
     NSAssert([value isKindOfClass:[NSString class]],
              @"%@ is not an NSString.", value);
     nativeConstraints.push_back(webrtc::MediaConstraintsInterface::Constraint(
         key.stdString, value.stdString));
   }
   return nativeConstraints;
 }
 
 @end