Revert of SkPDF: Move SkFlate into src/pdf (part 1/3) (patchset #1 id:1 of https://codereview.chromium.org/1285913002/ )

Reason for revert:
broke gn ("Duplicate object file")

Original issue's description:
> SkPDF:  Move SkFlate into src/pdf (part 1/3)
>
> Next, we change Chromium build files, then we do the actual move.
>
> Committed: https://skia.googlesource.com/skia/+/e14c1fe04fc72ec9bcf55820b5c65a71d7d0a764

TBR=bungeman@google.com
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true

Review URL: https://codereview.chromium.org/1289863002

gyp/pdf.gyp

@@ -20,7 +20,7 @@
       'variables': { 'skia_pdf_use_sfntly%': 1, },
       'dependencies': [
         'skia_lib.gyp:skia_lib',
-        'zlib.gyp:zlib',
+        'skflate.gyp:skflate',
       ],
       'includes': [
         'pdf.gypi',

gyp/pdf.gypi

@@ -11,9 +11,6 @@
 #
 {
     'sources': [
-        # TODO(halcanary): Move to <(skia_src_path)/pdf.
-        '<(skia_src_path)/core/SkFlate.cpp',
-
         '<(skia_src_path)/doc/SkDocument_PDF.cpp',
         '<(skia_src_path)/pdf/SkJpegInfo.cpp',
         '<(skia_src_path)/pdf/SkJpegInfo.h',

gyp/skflate.gyp

@@ -0,0 +1,18 @@
+# Copyright 2015 Google Inc.
+#
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+# Target for including SkFlate.
+{
+  'targets': [
+    {
+      'target_name': 'skflate',
+      'type': 'static_library',
+      'dependencies': [
+        'skia_lib.gyp:skia_lib',
+        'zlib.gyp:zlib',
+      ],
+      'sources': [ '../src/core/SkFlate.cpp' ],
+    },
+  ],
+}