Add missing header files to GN files

third_party/WebKit/Source/core/page/BUILD.gn

Index: third_party/WebKit/Source/core/page/BUILD.gn
diff --git a/third_party/WebKit/Source/core/page/BUILD.gn b/third_party/WebKit/Source/core/page/BUILD.gn
index 3016a67f5befbac55056717d0b4ae25452fe1804..ad88d7ec1a037243989c93166ed5b16d802ee51c 100644
--- a/third_party/WebKit/Source/core/page/BUILD.gn
+++ b/third_party/WebKit/Source/core/page/BUILD.gn
@@ -22,6 +22,7 @@ blink_core_sources("page") {
     "DragController.cpp",
     "DragController.h",
     "DragData.cpp",
+    "DragData.h",
     "DragSession.h",
     "DragState.h",
     "EditorClient.h",
@@ -36,6 +37,7 @@ blink_core_sources("page") {
     "Page.h",
     "PageAnimator.cpp",
     "PageAnimator.h",
+    "PagePopup.h",
     "PagePopupClient.cpp",
     "PagePopupClient.h",
     "PagePopupController.cpp",
@@ -46,6 +48,7 @@ blink_core_sources("page") {
     "PageVisibilityNotifier.h",
     "PageVisibilityObserver.h",
     "PageVisibilityState.cpp",
+    "PageVisibilityState.h",
     "PointerLockController.cpp",
     "PointerLockController.h",
     "PopupOpeningObserver.h",
@@ -62,6 +65,7 @@ blink_core_sources("page") {
     "TouchDisambiguation.h",
     "ValidationMessageClient.h",
     "WindowFeatures.cpp",
+    "WindowFeatures.h",
     "scrolling/OverscrollController.cpp",
     "scrolling/OverscrollController.h",
     "scrolling/RootScrollerController.cpp",