SkPDF:  Move SkFlate into src/pdf (part 1/3) [reland]

Rename to SkDeflate so Chromium builders continue to work

Next, we change remove SkFlate from Chromium build files, then we can delete SkFlate.

Review URL: https://codereview.chromium.org/1285913002
diff --git a/gyp/pdf.gypi b/gyp/pdf.gypi
index 0c9cb06..f114fa7 100644
--- a/gyp/pdf.gypi
+++ b/gyp/pdf.gypi
@@ -12,6 +12,8 @@
 {
     'sources': [
         '<(skia_src_path)/doc/SkDocument_PDF.cpp',
+        '<(skia_src_path)/pdf/SkDeflate.cpp',
+        '<(skia_src_path)/pdf/SkDeflate.h',
         '<(skia_src_path)/pdf/SkJpegInfo.cpp',
         '<(skia_src_path)/pdf/SkJpegInfo.h',
         '<(skia_src_path)/pdf/SkPDFBitmap.cpp',