Tweaks to vs_toolchain to simplify it, and support gn VS 2015

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/ccache.gni")
 
@@ skipping 595 matching lines @@
   cflags_cc = []
 
   if (is_win) {
     if (treat_warnings_as_errors) {
       cflags += [ "/WX" ]
     }
 
     cflags += [
       # Warnings permanently disabled:
 
+      # C4091: 'typedef ': ignored on left of 'X' when no variable is
+      #                    declared.
+      # This happens in a number of Windows headers. Dumb.
+      "/wd4091",
+
       # C4127: conditional expression is constant
       # This warning can in theory catch dead code and other problems, but
       # triggers in far too many desirable cases where the conditional
       # expression is either set by macros or corresponds some legitimate
       # compile-time constant expression (due to constant template args,
       # conditionals comparing the sizes of different types, etc.).  Some of
       # these can be worked around, but it's not worth it.
       "/wd4127",
 
       # C4251: 'identifier' : class 'type' needs to have dll-interface to be
@@ skipping 44 matching lines @@
       # Warnings to evaluate and possibly fix/reenable later:
 
       "/wd4100",  # Unreferenced formal function parameter.
       "/wd4121",  # Alignment of a member was sensitive to packing.
       "/wd4244",  # Conversion: possible loss of data.
       "/wd4481",  # Nonstandard extension: override specifier.
       "/wd4505",  # Unreferenced local function has been removed.
       "/wd4510",  # Default constructor could not be generated.
       "/wd4512",  # Assignment operator could not be generated.
       "/wd4610",  # Class can never be instantiated, constructor required.
+      "/wd4838",  # Narrowing conversion. Doesn't seem to be very useful.
       "/wd4995",  # 'X': name was marked as #pragma deprecated
       "/wd4996",  # Deprecated function warning.
+
+      # These are variable shadowing warnings that are new in VS2015. We
+      # should work through these at some point -- they may be removed from
+      # the RTM release in the /W4 set.
+      "/wd4456",
+      "/wd4457",
+      "/wd4458",
+      "/wd4459",
     ]
 
     # VS xtree header file needs to be patched or 4702 (unreachable code
     # warning) is reported if _HAS_EXCEPTIONS=0. Disable the warning if xtree is
     # not patched.
     if (!msvs_xtree_patched &&
         exec_script("../../win_is_xtree_patched.py", [], "value") == 0) {
       cflags += [ "/wd4702" ]  # Unreachable code.
     }
 
@@ skipping 544 matching lines @@
   if (symbol_level == 0) {
     configs = [ ":no_symbols" ]
   } else if (symbol_level == 1) {
     configs = [ ":minimal_symbols" ]
   } else if (symbol_level == 2) {
     configs = [ ":symbols" ]
   } else {
     assert(false)
   }
 }