keep only one typedef for the native drawing context

This patch remove the NativeDrawingContext from ui/gfx/native_widget_types.h,
renames the PlatformSurface in skia/ext/platform_surface.h to NativeDrawingContext,
and updates the clients of gfx::NativeDrawingContext to the skia one.

BUG=76105
TEST=skia_unittests,printing_unittests
[email protected],[email protected],[email protected]
[email protected]

Review-Url: https://codereview.chromium.org/2400873002
Cr-Commit-Position: refs/heads/master@{#424585}
diff --git a/printing/printed_document_mac.cc b/printing/printed_document_mac.cc
index 3710d62..73286966 100644
--- a/printing/printed_document_mac.cc
+++ b/printing/printed_document_mac.cc
@@ -14,7 +14,8 @@
 namespace printing {
 
 void PrintedDocument::RenderPrintedPage(
-    const PrintedPage& page, gfx::NativeDrawingContext context) const {
+    const PrintedPage& page,
+    skia::NativeDrawingContext context) const {
 #ifndef NDEBUG
   {
     // Make sure the page is from our list.