Wire up download attribution enable finch experiment

chrome/browser/safe_browsing/safe_browsing_navigation_observer.cc

Index: chrome/browser/safe_browsing/safe_browsing_navigation_observer.cc
diff --git a/chrome/browser/safe_browsing/safe_browsing_navigation_observer.cc b/chrome/browser/safe_browsing/safe_browsing_navigation_observer.cc
index 3efb350d843e7954457c40c329b6ebb084f7e972..eec6206684cf9f7536011126830e9ed5a82a768a 100644
--- a/chrome/browser/safe_browsing/safe_browsing_navigation_observer.cc
+++ b/chrome/browser/safe_browsing/safe_browsing_navigation_observer.cc
@@ -70,13 +70,14 @@ NavigationEvent::~NavigationEvent() {}
 // SafeBrowsingNavigationObserver --------------------------------------------
 
 // static
-void SafeBrowsingNavigationObserver::MaybeCreateForWebContents(
-    content::WebContents* web_contents) {
-  if (FromWebContents(web_contents))
-    return;
-  // TODO(jialiul): This method will be called by TabHelpers::AttachTabHelpers.
-  // Complete this method when the entire class is ready.
-  NOTIMPLEMENTED();
+void SafeBrowsingNavigationObserver::CreateForWebContents(
+    content::WebContents* web_contents,
+    const scoped_refptr<SafeBrowsingNavigationObserverManager>& manager) {
+  if (!FromWebContents(web_contents)) {
+    web_contents->SetUserData(
+        kWebContentsUserDataKey,
+        new SafeBrowsingNavigationObserver(web_contents, manager));
+  }
 }
 
 // static
@@ -115,11 +116,13 @@ void SafeBrowsingNavigationObserver::DidStartNavigation(
          !SafeBrowsingNavigationObserverManager::IsUserGestureExpired(
              last_user_gesture_timestamp_)) ||
         !navigation_handle->IsRendererInitiated()) {
-      nav_event.is_user_initiated = has_user_gesture_;
-      manager_->OnUserGestureConsumed(web_contents(),
-                                      last_user_gesture_timestamp_);
+      nav_event.is_user_initiated = true;
+      if (has_user_gesture_) {
+        manager_->OnUserGestureConsumed(web_contents(),
+                                        last_user_gesture_timestamp_);
+        has_user_gesture_ = false;

[Nathan Parker, 2016/12/20 01:01:33]

So this consumes the user gesture only if there really was one... correct?  Just
trying to make sure I understand it.

[Jialiu Lin, 2016/12/20 02:07:51]

Yes. That's correct.

+      }
     }
-    has_user_gesture_ = false;
   }
 
   // All the other fields are reconstructed based on current content of