Make absolute and sort all Sky headers

sky/engine/public/BUILD.gn

 # Copyright 2014 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("//tools/grit/grit_rule.gni")
 
 group("test_support") {
   deps = [
     "//sky/engine/web:test_support",
   ]
 }
 
-config("sky_headers_config") {
-  include_dirs = [ ".." ]
-}
-
-# Depend on this target to use public sky API headers for things like enums
-# and public structures without actually linking against any Blink libraries.
-source_set("sky_headers") {
-  direct_dependent_configs = [
-    ":sky_headers_config",
-  ]
-
+source_set("platform_headers") {
   public = [
     "platform/Platform.h",
     "platform/ServiceProvider.h",
     "platform/WebArrayBuffer.h",
     "platform/WebBlendMode.h",
     "platform/WebCString.h",
     "platform/WebCallbacks.h",
     "platform/WebCanvas.h",
     "platform/WebClipboard.h",
     "platform/WebColor.h",
@@ skipping 66 matching lines @@
     "platform/WebURLLoaderClient.h",
     "platform/WebURLRequest.h",
     "platform/WebURLResponse.h",
     "platform/WebUnitTestSupport.h",
     "platform/WebVector.h",
     "platform/android/WebSandboxSupport.h",
     "platform/linux/WebFallbackFont.h",
     "platform/linux/WebFontInfo.h",
     "platform/linux/WebFontRenderStyle.h",
     "platform/linux/WebSandboxSupport.h",
+  ]
+}
+
+source_set("web_headers") {
+  public = [
     "web/Sky.h",
     "web/WebActiveWheelFlingParameters.h",
     "web/WebArrayBufferConverter.h",
     "web/WebArrayBufferView.h",
     "web/WebBeginFrameArgs.h",
     "web/WebCache.h",
     "web/WebCachedURLRequest.h",
     "web/WebCompositionUnderline.h",
     "web/WebConsoleMessage.h",
     "web/WebContentDetectionResult.h",
@@ skipping 42 matching lines @@
     "web/WebURLLoaderOptions.h",
     "web/WebUserGestureIndicator.h",
     "web/WebUserGestureToken.h",
     "web/WebView.h",
     "web/WebViewClient.h",
     "web/WebWidget.h",
     "web/WebWidgetClient.h",
     "web/linux/WebFontRendering.h",
   ]
 }