Fix the handling of user gestures for external protocol handler dialogs.

chrome/browser/external_protocol/external_protocol_handler.cc

Index: chrome/browser/external_protocol/external_protocol_handler.cc
diff --git a/chrome/browser/external_protocol/external_protocol_handler.cc b/chrome/browser/external_protocol/external_protocol_handler.cc
index b414261cb32dd576f655e6e8529eba46d817e917..528d21d82f801e5fff1c8c1f2cbd9d5dd756051e 100644
--- a/chrome/browser/external_protocol/external_protocol_handler.cc
+++ b/chrome/browser/external_protocol/external_protocol_handler.cc
@@ -27,10 +27,10 @@
 
 using content::BrowserThread;
 
-// Whether we accept requests for launching external protocols. This is set to
-// false every time an external protocol is requested, and set back to true on
-// each user gesture. This variable should only be accessed from the UI thread.
-static bool g_accept_requests = true;
+// User gesture counter. This is increased when a user gesture is available, and
+// decreased when the gesture is consumed or goes out of scope. This variable
+// should only be accessed from the UI thread.
+static size_t g_consumable_user_gestures = 0;
 
 namespace {
 
@@ -204,8 +204,8 @@ void ExternalProtocolHandler::PrepopulateDictionary(
 // static
 ExternalProtocolHandler::BlockState ExternalProtocolHandler::GetBlockState(
     const std::string& scheme) {
-  // If we are being carpet bombed, block the request.
-  if (!g_accept_requests)
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
+  if (!g_consumable_user_gestures)
     return BLOCK;
 
   if (scheme.length() == 1) {
@@ -270,8 +270,6 @@ void ExternalProtocolHandler::LaunchUrlWithDelegate(const GURL& url,
     return;
   }
 
-  g_accept_requests = false;
-
   // The worker creates tasks with references to itself and puts them into
   // message loops. When no tasks are left it will delete the observer and
   // eventually be deleted itself.
@@ -309,8 +307,12 @@ void ExternalProtocolHandler::RegisterPrefs(PrefRegistrySimple* registry) {
   registry->RegisterDictionaryPref(prefs::kExcludedSchemes);
 }
 
-// static
-void ExternalProtocolHandler::PermitLaunchUrl() {
-  DCHECK(base::MessageLoopForUI::IsCurrent());
-  g_accept_requests = true;
+ExternalProtocolHandler::ScopedUserGesture::ScopedUserGesture() {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
+  g_consumable_user_gestures++;
+}
+
+ExternalProtocolHandler::ScopedUserGesture::~ScopedUserGesture() {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
+  g_consumable_user_gestures--;
 }