Add hooks for BeforeInstallPromptEvent to be redispatched.

Source/modules/app_banner/BeforeInstallPromptEvent.cpp

Index: Source/modules/app_banner/BeforeInstallPromptEvent.cpp
diff --git a/Source/modules/app_banner/BeforeInstallPromptEvent.cpp b/Source/modules/app_banner/BeforeInstallPromptEvent.cpp
index a11e7cd5a000f3bdb356628b4544d541f294dc86..607acc0c63c718ad1f6042fb2948533c0e5d9456 100644
--- a/Source/modules/app_banner/BeforeInstallPromptEvent.cpp
+++ b/Source/modules/app_banner/BeforeInstallPromptEvent.cpp
@@ -22,6 +22,7 @@ BeforeInstallPromptEvent::BeforeInstallPromptEvent(const AtomicString& name, con
     , m_platforms(platforms)
     , m_requestId(requestId)
     , m_client(client)
+    , m_redispatched(false)
 {
 }
 
@@ -30,6 +31,7 @@ BeforeInstallPromptEvent::BeforeInstallPromptEvent(const AtomicString& name, con
     , m_platforms(init.platforms())
     , m_requestId(-1)
     , m_client(nullptr)
+    , m_redispatched(false)
 {
 }
 
@@ -59,4 +61,20 @@ const AtomicString& BeforeInstallPromptEvent::interfaceName() const
     return EventNames::BeforeInstallPromptEvent;
 }
 
+ScriptPromise BeforeInstallPromptEvent::prompt(ScriptState* scriptState)
+{
+    RefPtrWillBeRawPtr<ScriptPromiseResolver> resolver = ScriptPromiseResolver::create(scriptState);
+    ScriptPromise promise = resolver->promise();

[mlamouri (slow - plz ping), 2015/06/11 00:42:17]

You probably don't need a |resolver| or a |promise| here. You could simply call
ScriptPromise::cast() and ScriptPromise::reject().

+    if (m_client && defaultPrevented() && !m_redispatched) {
+        ASSERT(m_requestId != -1);
+        m_redispatched = true;
+        m_client->resolveEventRedispatch(m_requestId);
+        resolver->resolve();
+        userChoice(scriptState);

[mlamouri (slow - plz ping), 2015/06/11 00:42:17]

Why do you call that?

+    } else {
+        resolver->reject();

[mlamouri (slow - plz ping), 2015/06/11 00:42:17]

I think you should reject with an InvalidState error.

+    }
+    return promise;
+}
+
 } // namespace blink