Revert of Enable C4018 globally for the GN build, and disable per-target. (patchset #4 id:60001 of https://codereview.chromium.org/1246103007/)

Reason for revert:
Speculative revert based on windows gn bots failing with

http://build.chromium.org/p/chromium.win/builders/Win8%20GN%20%28dbg%29/builds/10113

FAILED: ninja -t msvc -e environment.x64 -- E:\b\build\goma/gomacc.exe "E:\b\depot_tools\win_toolchain\vs2013_files\VC\bin\amd64/cl.exe" /nologo /showIncludes /FC @obj/base/base/precompile.c.obj.rsp /c ../../build/precompile.cc /Foobj/base/base/precompile.c.obj /Fdobj/base/base_c.pdb
e:\b\build\slave\win_x64_gn__dbg_\build\src\build\precompile.cc(8) : error C2220: warning treated as error - no 'object' file generated
e:\b\build\slave\win_x64_gn__dbg_\build\src\build\precompile.cc(8) : warning C4206: nonstandard extension used : translation unit is empty
ninja: build stopped: subcommand failed.

In theory this warning shouldn't have affected other warnings, but there are no other clear candidates.

Original issue's description:
> Enable C4018 globally for the GN build, and disable per-target.
>
> This matches what the GYP build does.
>
> BUG=398202
> TEST=none
>
> Committed: https://crrev.com/d408e1965f8e03629738039289ab7779c42a318c
> Cr-Commit-Position: refs/heads/master@{#340590}

TBR=brettw@chromium.org,erg@chromium.org,pkasting@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=398202

Review URL: https://codereview.chromium.org/1257583007

Cr-Commit-Position: refs/heads/master@{#340623}

10 files changed, 14 insertions, 26 deletions

diff --git a/build/config/compiler/BUILD.gn b/build/config/compiler/BUILD.gn
index 86d1586..4cc958c 100644
--- a/build/config/compiler/BUILD.gn
+++ b/build/config/compiler/BUILD.gn
@@ -717,6 +717,11 @@ if (is_win) {
 
     # Warnings permanently disabled:
 
+    # TODO(GYP) The GYP build doesn't have this globally enabled but disabled
+    # for a bunch of individual targets. Re-enable this globally when those
+    # targets are fixed.
+    "/wd4018",  # Comparing signed and unsigned values.
+
     # 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
diff --git a/components/filesystem/file_impl.cc b/components/filesystem/file_impl.cc
index 4925f9a..2539498 100644
--- a/components/filesystem/file_impl.cc
+++ b/components/filesystem/file_impl.cc
@@ -102,7 +102,7 @@ void FileImpl::Write(mojo::Array<uint8_t> bytes_to_write,
   // actually wrote that much).
   if (bytes_to_write.size() >
 #if defined(OS_WIN)
-      static_cast<size_t>(std::numeric_limits<int>::max())) {
+      std::numeric_limits<INT>::max()) {
 #else
       static_cast<size_t>(std::numeric_limits<ssize_t>::max())) {
 #endif
diff --git a/third_party/leveldatabase/BUILD.gn b/third_party/leveldatabase/BUILD.gn
index b3080d8..c29f0f8 100644
--- a/third_party/leveldatabase/BUILD.gn
+++ b/third_party/leveldatabase/BUILD.gn
@@ -113,10 +113,6 @@ static_library("leveldatabase") {
     "//third_party/re2",
     "//third_party/snappy",
   ]
-
-  if (is_win) {
-    cflags = [ "/wd4018" ]  # Signed/unsigned mismatch in comparison.
-  }
 }
 
 if (!is_android) {
diff --git a/third_party/libexif/BUILD.gn b/third_party/libexif/BUILD.gn
index 8eba113..5a464e6 100644
--- a/third_party/libexif/BUILD.gn
+++ b/third_party/libexif/BUILD.gn
@@ -60,7 +60,7 @@ if (!is_linux || is_chromeos) {
 
       ldflags = [ "/DEF:" + rebase_path("libexif.def") ]
 
-      cflags = [ "/wd4018" ]  # Signed/unsigned mismatch in comparison.
+      cflags = [ "/wd4018" ]  # size/unsigned mismatch
 
       # TODO(GYP): Handle /analyze switch, when it will be used in GN.
     } else if (is_linux) {
diff --git a/third_party/libxml/BUILD.gn b/third_party/libxml/BUILD.gn
index 58a5f1c..1f10dee 100644
--- a/third_party/libxml/BUILD.gn
+++ b/third_party/libxml/BUILD.gn
@@ -155,10 +155,7 @@ static_library("libxml") {
   ]
 
   if (is_win) {
-    cflags_c = [
-      "/wd4018",  # Signed/unsigned mismatch in comparison.
-      "/wd4101",  # Unreferenced local variable.
-    ]
+    cflags_c = [ "/wd4101" ]  # Unreferenced local variable.
   } else if (is_mac || is_ios || is_android) {
     # http://www.xmlsoft.org/threads.html says that this is required when using
     # libxml from several threads, which can possibly happen in chrome. On
diff --git a/third_party/mesa/BUILD.gn b/third_party/mesa/BUILD.gn
index 62f8611..96f5ec0 100644
--- a/third_party/mesa/BUILD.gn
+++ b/third_party/mesa/BUILD.gn
@@ -125,7 +125,6 @@ config("mesa_internal_warnings") {
     cflags += [
       "-Wno-tautological-constant-out-of-range-compare",
       "-Wno-mismatched-tags",  # Fixed upstream.
-
       # mesa's STATIC_ASSERT() macro expands to an ununused typedef.
       "-Wno-unused-local-typedef",
     ]
@@ -135,7 +134,6 @@ config("mesa_internal_warnings") {
     # Mesa is ever rolled and the warnings are fixed.
     cflags += [
       "/wd4005",  # Macro defined twice.
-      "/wd4018",  # Signed/unsigned mismatch in comparison.
       "/wd4065",  # Switch statement contains 'default' but no 'case' labels.
       "/wd4090",  # 'Operation' : different 'modifier' qualifiers
       "/wd4099",  # Type name struct-vs-class doesn't match.
diff --git a/third_party/protobuf/BUILD.gn b/third_party/protobuf/BUILD.gn
index 7d42a00d..0c57bd6 100644
--- a/third_party/protobuf/BUILD.gn
+++ b/third_party/protobuf/BUILD.gn
@@ -77,11 +77,11 @@ protobuf_lite_sources = [
 protobuf_lite_cflags = []
 if (is_win) {
   protobuf_lite_cflags = [
-    "/wd4018",  # Signed/unsigned mismatch in comparison.
-    "/wd4244",  # Implicit conversion, possible loss of data.
-    "/wd4355",  # 'this' used in base member initializer list.
-    "/wd4267",  # Size_t to int truncation.
-    "/wd4291",  # No matching operator delete for a placement new.
+    "/wd4018",  # signed/unsigned mismatch in comparison
+    "/wd4244",  # implicit conversion, possible loss of data
+    "/wd4355",  # 'this' used in base member initializer list
+    "/wd4267",  # size_t to int truncation
+    "/wd4291",  # no matching operator delete for a placement new
   ]
 }
 
diff --git a/third_party/qcms/BUILD.gn b/third_party/qcms/BUILD.gn
index a4b60d3..5e27d44 100644
--- a/third_party/qcms/BUILD.gn
+++ b/third_party/qcms/BUILD.gn
@@ -32,7 +32,6 @@ source_set("qcms") {
 
   if (is_win) {
     cflags = [
-      "/wd4018",  # Signed/unsigned mismatch in comparison.
       "/wd4056",  # Overflow in floating-point constant arithmetic (INFINITY).
       "/wd4756",  # Overflow in constant arithmetic (INFINITY).
     ]
diff --git a/third_party/re2/BUILD.gn b/third_party/re2/BUILD.gn
index ca1f7a2..2bc130a 100644
--- a/third_party/re2/BUILD.gn
+++ b/third_party/re2/BUILD.gn
@@ -67,10 +67,7 @@ static_library("re2") {
 
   if (is_win) {
     include_dirs = [ "mswin" ]
-    cflags = [
-      "/wd4018",  # Signed/unsigned mismatch in comparison.
-      "/wd4722",  # Destructor never terminates.
-    ]
+    cflags = [ "/wd4722" ]  # Destructor never terminates.
   } else {
     sources -= [ "mswin/stdint.h" ]
   }
diff --git a/third_party/snappy/BUILD.gn b/third_party/snappy/BUILD.gn
index e8de575..4af0e81 100644
--- a/third_party/snappy/BUILD.gn
+++ b/third_party/snappy/BUILD.gn
@@ -31,10 +31,6 @@ static_library("snappy") {
   configs += [ "//build/config/compiler:no_chromium_code" ]
   public_configs = [ ":snappy_config" ]
 
-  if (is_win) {
-    cflags = [ "/wd4018" ]  # Signed/unsigned mismatch in comparison.
-  }
-
   if (is_clang) {
     # snappy-stubs-internal.h unapologetically has: using namespace std
     # https://code.google.com/p/snappy/issues/detail?id=70