Add a NavigationThrottle to the public content/ interface

content/public/browser/content_browser_client.h

Index: content/public/browser/content_browser_client.h
diff --git a/content/public/browser/content_browser_client.h b/content/public/browser/content_browser_client.h
index f45cd7b3c7bcdbad417e54ea39fda8c42d3c056f..5c5f2a779043cf900c7599297b1f1aff6d6ecbd1 100644
--- a/content/public/browser/content_browser_client.h
+++ b/content/public/browser/content_browser_client.h
@@ -98,6 +98,7 @@ class LocationProvider;
 class MediaObserver;
 class NavigatorConnectContext;
 class NavigatorConnectServiceFactory;
+class NavigationHandle;
 class PlatformNotificationService;
 class PresentationServiceDelegate;
 class QuotaPermissionContext;
@@ -652,6 +653,13 @@ class CONTENT_EXPORT ContentBrowserClient {
   // Allows the embedder to record |metric| for a specific |url|.
   virtual void RecordURLMetric(const std::string& metric, const GURL& url) {}
 
+  // Allows the embedder to register NavigationThrottles for a navigation.

[nasko, 2015/08/31 23:25:15]

nit: s/NavigationThrottles/one or more NavigationThrottle/

[clamy, 2015/09/03 15:30:52]

Done.

+  // NavigationThrottles are used to control the flow of a navigation on the UI

[nasko, 2015/08/31 23:25:15]

nit: Singular NavigationThrottle.

[clamy, 2015/09/03 15:30:52]

Done.

+  // thread. The embedder is guaranteed that the throttles will be executed in
+  // the order they were registered.

[nasko, 2015/08/31 23:25:15]

The order is guaranteed for each embedder, but embedders order isn't, right?

[Avi (use Gerrit), 2015/09/01 16:38:47]

What do you mean by that question? There is always exactly one embedder.

+  virtual void AddNavigationThrottles(NavigationHandle* navigation_handle,
+                                      WebContents* web_contents) {}

[davidben, 2015/09/01 21:55:18]

It's a little odd that this API is called AddNavigationThrottles, but it's not
really specific to navigation throttles. It seems to just be a thing that
signals a particular point in the timeline (start of navigation or so).

[clamy, 2015/09/03 15:30:52]

Due to changes to the NavigationHandle interface, it now returns a vector of
NavigationThrottles. I think it makes more sense now.

+
   // Populates |mappings| with all files that need to be mapped before launching
   // a child process.
 #if defined(OS_ANDROID)