Change beforeinstallprompt event to take an array of platforms.

public/web/WebLocalFrame.h

Index: public/web/WebLocalFrame.h
diff --git a/public/web/WebLocalFrame.h b/public/web/WebLocalFrame.h
index 72be9be027a3d3374333f3127deeb89687edc365..61e4ee7f37dd5c9fe69f8e1591d164065d789d5b 100644
--- a/public/web/WebLocalFrame.h
+++ b/public/web/WebLocalFrame.h
@@ -128,9 +128,13 @@ public:
 
     // App banner -------------------------------------------------------------
 
-    // Request to show an application install banner for the given |platform|.
+    // Request to show an application install banner for the given |platforms|.
     // The implementation can request the embedder to cancel the call by setting
     // |cancel| to true.
+    virtual void willShowInstallBannerPrompt(const WebVector<WebString>& platforms, WebAppBannerPromptReply*) = 0;
+
+    // Version of the above which takes a single platform.
+    // TODO(benwells): remove this once the chrome side has been updated.
     virtual void willShowInstallBannerPrompt(const WebString& platform, WebAppBannerPromptReply*) = 0;
 };