Presentation API: ignore page visibility changes if ExecutionContext is destoyed.

PresentationAvailability is listening to the page visibility but is using
the ExecutionContext to send messages to the controller. The ExecutionContext
might be destroyed before a page visibility change, for example, if the object
was created in a frame that has been removed from the frame tree.

BUG=526923,526116

Review URL: https://codereview.chromium.org/1322493006

git-svn-id: svn://svn.chromium.org/blink/trunk@201918 bbb929c8-8fbe-4397-9dbb-9b2b20218538

1 files changed, 2 insertions, 1 deletions

diff --git a/third_party/WebKit/public/platform/modules/presentation/WebPresentationAvailabilityObserver.h b/third_party/WebKit/public/platform/modules/presentation/WebPresentationAvailabilityObserver.h
index e70e766..49d6835 100644
--- a/third_party/WebKit/public/platform/modules/presentation/WebPresentationAvailabilityObserver.h
+++ b/third_party/WebKit/public/platform/modules/presentation/WebPresentationAvailabilityObserver.h
@@ -5,6 +5,7 @@
 #ifndef WebPresentationAvailabilityObserver_h
 #define WebPresentationAvailabilityObserver_h
 
+#include "public/platform/WebCommon.h"
 #include "public/platform/WebURL.h"
 
 namespace blink {
@@ -12,7 +13,7 @@ namespace blink {
 // WebPresentationAvailabilityObserver is an interface that is implemented by
 // objects that wish to be notified when there is a presentation display
 // availability change for a given URL.
-class WebPresentationAvailabilityObserver {
+class BLINK_PLATFORM_EXPORT WebPresentationAvailabilityObserver {
 public:
     virtual ~WebPresentationAvailabilityObserver() = default;