Add constants for PDF 1.7 spec, table 8.15.

BUG=pdfium:1049

Change-Id: I09fb1c34b8f08ce5c5b5f86e7fe64dfd11ed770d
Reviewed-on: https://pdfium-review.googlesource.com/c/49571
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>
diff --git a/constants/BUILD.gn b/constants/BUILD.gn
index 25a574e..cdfd665 100644
--- a/constants/BUILD.gn
+++ b/constants/BUILD.gn
@@ -7,6 +7,7 @@
 
 jumbo_source_set("constants") {
   sources = [
+    "annotation_common.h",
     "form_flags.h",
     "page_object.h",
     "stream_dict_common.h",
diff --git a/constants/annotation_common.h b/constants/annotation_common.h
new file mode 100644
index 0000000..8973360
--- /dev/null
+++ b/constants/annotation_common.h
@@ -0,0 +1,30 @@
+// Copyright 2019 PDFium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CONSTANTS_ANNOTATION_COMMON_H_
+#define CONSTANTS_ANNOTATION_COMMON_H_
+
+namespace pdfium {
+namespace annotation {
+
+// PDF 1.7 spec, table 8.15.
+// Entries common to all annotation dictionaries.
+
+constexpr char kType[] = "Type";
+constexpr char kSubtype[] = "Subtype";
+constexpr char kRect[] = "Rect";
+constexpr char kContents[] = "Contents";
+constexpr char kP[] = "P";
+constexpr char kNM[] = "NM";
+constexpr char kM[] = "M";
+constexpr char kF[] = "F";
+constexpr char kAP[] = "AP";
+constexpr char kAS[] = "AS";
+constexpr char kBorder[] = "Border";
+constexpr char kC[] = "C";
+
+}  // namespace annotation
+}  // namespace pdfium
+
+#endif  // CONSTANTS_ANNOTATION_COMMON_H_