[gn] Enable stricter build flags

BUILD.gn

Index: BUILD.gn
diff --git a/BUILD.gn b/BUILD.gn
index 568ab50f344e1dcf152df61dcb5a29f0e11f1e9c..5fad86ff24816334ed1b5cf9c42da3e9ab3146be 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -463,6 +463,20 @@ config("toolchain") {
     #  cflags += [ "-Wshorten-64-to-32" ]
     #}
   }
+
+  if (is_win) {
+    cflags += [

[jgruber, 2017/03/17 13:21:20]

4267, 4245: Pedantic conversion warnings. We might want to fix these, but this
would be another mismatch between windows bot builds and local builds.
4324: This seems like an FYI, nothing wrong with this pattern.
4701, 4703: Some false positives, and all over our code. May want to fix this.
4702: Can't handle our UNREACHABLE() macro.
4709: Windows compiler bug.
4718: Seems like FYI.
4800: Pedantic warning that triggers e.g. on static_cast<bool>(int).

+      "/wd4267",  # Conversion with possible loss of data.
+      "/wd4245",  # Conversion with signed/unsigned mismatch.
+      "/wd4324",  # Padding structure due to alignment.
+      "/wd4701",  # Potentially uninitialized local variable.
+      "/wd4702",  # Unreachable code.
+      "/wd4703",  # Potentially uninitialized local pointer variable.
+      "/wd4709",  # Comma operator within array index expr (bugged).
+      "/wd4718",  # Recursive call has no side-effect.
+      "/wd4800",  # Forcing value to bool.
+    ]
+  }
 }
 
 ###############################################################################
@@ -2289,11 +2303,6 @@ v8_source_set("v8_base") {
   sources += [ v8_generated_peephole_source ]
   deps += [ ":run_mkpeephole" ]
 
-  if (is_win) {
-    # TODO(jschuh): crbug.com/167187 fix size_t to int truncations.
-    cflags = [ "/wd4267" ]
-  }
-
   if (v8_enable_i18n_support) {
     deps += [ "//third_party/icu" ]
     if (is_win) {