Increase minimum iOS version requirements to iOS 9.0.

build/config/ios/ios_sdk.gni

 # Copyright 2015 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.
 
 declare_args() {
   # SDK path to use. When empty this will use the default SDK based on the
   # value of use_ios_simulator.
   ios_sdk_path = ""
 
   use_ios_simulator = target_cpu == "x86" || target_cpu == "x64"
 
   # Version of iOS that we're targeting.
-  ios_deployment_target = "7.0"
+  ios_deployment_target = "9.0"
 
   # The iOS Code signing identity to use
   # TODO(GYP), TODO(sdfresne): Consider having a separate
   # ios_enable_code_signing_flag=<bool> flag to make the invocation clearer.
   ios_enable_code_signing = true
   ios_code_signing_identity = ""
 }
 
 if (ios_sdk_path == "") {
   # Compute default target.
@@ skipping 20 matching lines @@
     ios_code_signing_identity = _ios_identities[0]
   }
 
   if (ios_code_signing_identity == "") {
     print("Tried to prepare a device build without specifying a code signing")
     print("identity and could not detect one automatically either.")
     print("TIP: Simulator builds dont require code signing...")
     assert(false)
   }
 }