Enable -Wundeclared-selector on ios.

build/config/compiler/BUILD.gn

 # Copyright (c) 2013 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("//build/config/android/config.gni")
 import("//build/config/chrome_build.gni")
 import("//build/config/compiler/compiler.gni")
 import("//build/config/nacl/config.gni")
 import("//build/toolchain/cc_wrapper.gni")
 import("//build/toolchain/toolchain.gni")
@@ skipping 952 matching lines @@
       ]
     }
   } else {
     if (is_mac && !is_nacl) {
       # When compiling Objective-C, warns if a method is used whose
       # availability is newer than the deployment target. This is not
       # required when compiling Chrome for iOS.
       cflags += [ "-Wpartial-availability" ]
     }
 
+    if (is_ios) {

[stkhapugin, 2016/12/23 10:27:18]

Can you ping someone in Chromium on Mac to look at this in case they want this
flag?

[marq (ping after 24h), 2016/12/23 10:33:06]

I will, but if the Mac code requires fixes as well, I don't want to complicate
this CL with them. So my thinking is that we can land this and start using it
for iOS, and if the Mac folks want to turn it on they can.

+      # When compiling Objective-C, warns if a selector named via @selector has
+      # not been defined in any visible interface.
+      cflags += [ "-Wundeclared-selector" ]
+    }
+
     # Suppress warnings about ABI changes on ARM (Clang doesn't give this
     # warning).
     if (current_cpu == "arm" && !is_clang) {
       cflags += [ "-Wno-psabi" ]
     }
 
     if (!is_clang) {
       cflags_cc += [
         # See comment for -Wno-c++11-narrowing.
         "-Wno-narrowing",
@@ skipping 656 matching lines @@
 
 if (is_ios || is_mac) {
   # On Mac and iOS, this enables support for ARC (automatic ref-counting).
   # See http://clang.llvm.org/docs/AutomaticReferenceCounting.html.
   config("enable_arc") {
     common_flags = [ "-fobjc-arc" ]
     cflags_objc = common_flags
     cflags_objcc = common_flags
   }
 }