Add headers to gn/gni files for all of sky/engine

sky/engine/BUILD.gn

Index: sky/engine/BUILD.gn
diff --git a/sky/engine/BUILD.gn b/sky/engine/BUILD.gn
index 4f8f0bec66464752ac2fb13b0310b8dd61cb5044..33eb367ec107693e7cc4bb4c72e78c83082b991a 100644
--- a/sky/engine/BUILD.gn
+++ b/sky/engine/BUILD.gn
@@ -38,31 +38,12 @@ config("config") {
   cflags = []
   defines = []
 
-  if (is_win) {
-    cflags += [
-      "/wd4065",  # Switch statement contains 'default' but no 'case' labels.
-                  # In generated parser code.
-      "/wd4305",  # Truncation from 'type1' to 'type2'.
-      "/wd4324",  # Struct padded due to declspec(align).
-      "/wd4702",  # Unreachable code, happens in bison-generated code.
-      "/wd4714",  # Function marked forceinline not inlined.
-      "/wd4800",  # Value forced to bool.
-      "/wd4996",  # Deprecated function call.
-    ]
-  }
-
-  if (is_win) {
-    if (component_mode == "shared_library") {
-      defines += [ "USING_V8_SHARED" ]
-    }
-  } else {  # ! Windows
-    # TODO(GYP) this should be based on gcc_version >= 46 but GN doesn't have a
-    # concept of GCC version yet.
+  # TODO(GYP) this should be based on gcc_version >= 46 but GN doesn't have a
+  # concept of GCC version yet.
 
-    # Disable warnings about c++0x compatibility, as some names (such as
-    # nullptr) conflict with upcoming c++0x types.
-    cflags_cc = [ "-Wno-c++0x-compat" ]
-  }
+  # Disable warnings about c++0x compatibility, as some names (such as
+  # nullptr) conflict with upcoming c++0x types.
+  cflags_cc = [ "-Wno-c++0x-compat" ]
 
   if (is_linux && cpu_arch == "arm") {
     # Due to a bug in gcc arm, we get warnings about uninitialized