Enable -Wshift-negative-value.

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/chromecast_build.gni")
 import("//build/config/compiler/compiler.gni")
 import("//build/config/nacl/config.gni")
 import("//build/toolchain/cc_wrapper.gni")
@@ skipping 1026 matching lines @@
       # Disables.
       "-Wno-missing-field-initializers",  # "struct foo f = {0};"
       "-Wno-unused-parameter",  # Unused function parameters.
     ]
   }
 
   if (is_chromeos) {
     # TODO(thakis): Remove, http://crbug.com/263960
     if (is_clang) {
       cflags_cc += [ "-Wno-reserved-user-defined-literal" ]
+
+      # TODO(thakis): Enable this, crbug.com/507717
+      if (!is_nacl) {
+        cflags += [ "-Wno-shift-negative-value" ]
+      }
     } else {
       cflags_cc += [ "-Wno-literal-suffix" ]
     }
   }
 
   if (is_clang) {
     cflags += [
       # TODO(thakis): Consider -Wloop-analysis (turns on
       # -Wrange-loop-analysis too).
 
@@ skipping 14 matching lines @@
 
       # TODO(thakis): This used to be implied by -Wno-unused-function,
       # which we no longer use. Check if it makes sense to remove
       # this as well. http://crbug.com/316352
       "-Wno-unneeded-internal-declaration",
 
       # TODO(hans): Get this cleaned up, http://crbug.com/428099
       "-Wno-inconsistent-missing-override",
     ]
 
-    # Chrome's hermetic Clang compiler, NaCl's Clang compiler and Xcode's Clang
-    # compiler will almost always have different versions. Certain flags may not
-    # be recognized by one version or the other.
-    if (!is_nacl) {
-      # Flags NaCl (Clang 3.7) does not recognize.
-      cflags += [
-        # TODO(thakis): Enable this, crbug.com/507717
-        "-Wno-shift-negative-value",
-      ]
-    }
-
     # use_xcode_clang only refers to the iOS toolchain, host binaries use
     # chromium's clang always.
     if (!is_nacl && (!use_xcode_clang || current_toolchain == host_toolchain)) {
       # Flags NaCl (Clang 3.7) and Xcode 7.3 (Clang clang-703.0.31) do not
       # recognize.
       cflags += [
         # TODO(thakis): https://crbug.com/604888
         "-Wno-undefined-var-template",
 
         # TODO(thakis): https://crbug.com/617318
@@ skipping 613 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
   }
 }