Enable PDF form saving for chromeos build.

Bug: 61248
Change-Id: Ib3a23abaa3ad6772c2af7cba6b333c33f901eb71
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1503905
Commit-Queue: dstockwell <dstockwell@chromium.org>
Auto-Submit: Lei Zhang <thestig@chromium.org>
Reviewed-by: dstockwell <dstockwell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#637921}

pdf/pdf_features.cc

@@ -7,8 +7,14 @@
 namespace chrome_pdf {
 namespace features {
 
-const base::Feature kSaveEditedPDFForm{"SaveEditedPDFForm",
-                                       base::FEATURE_DISABLED_BY_DEFAULT};
+const base::Feature kSaveEditedPDFForm {
+  "SaveEditedPDFForm",
+#if defined(OS_CHROMEOS)
+      base::FEATURE_ENABLED_BY_DEFAULT
+#else
+      base::FEATURE_DISABLED_BY_DEFAULT
+#endif  // defined(OS_CHROMEOS)
+};
 
 const base::Feature kPDFAnnotations {
   "PDFAnnotations",