[Windows MSVC CFG] Add support for CFG, and enable on chrome.exe & chrome_elf.dll.

build/config/win/BUILD.gn

Index: build/config/win/BUILD.gn
diff --git a/build/config/win/BUILD.gn b/build/config/win/BUILD.gn
index 9b6ac7423f2b9d4d12bdea8302a200507d706e6e..ebcbb10ce742238d4b8af82b28af907a73536934 100644
--- a/build/config/win/BUILD.gn
+++ b/build/config/win/BUILD.gn
@@ -264,6 +264,17 @@ config("common_linker_setup") {
   }
 }
 
+# Control Flow Guard (CFG)
+# https://msdn.microsoft.com/en-us/library/windows/desktop/mt637065.aspx
+config("win_msvc_cfg") {
+  # /DYNAMICBASE (ASLR) is turned off in debug builds, therefore CFG can’t be
+  # turned on either.
+  if (!is_clang && !is_debug) {
+    cflags = [ "/guard:cf" ]
+    ldflags = [ "/guard:cf" ]
+  }
+}
+
 # CRT --------------------------------------------------------------------------
 
 # Configures how the runtime library (CRT) is going to be used.