Remove VisitedLink dependency on rest of chrome

chrome/browser/visitedlink/visitedlink_delegate.h

+// Copyright (c) 2012 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CHROME_BROWSER_VISITEDLINK_VISITEDLINK_DELEGATE_H_
+#define CHROME_BROWSER_VISITEDLINK_VISITEDLINK_DELEGATE_H_
+
+class GURL;
+
+namespace content {
+class BrowserContext;
+}  // namespace content
+
+// Delegate class that clients of VisitedLinkMaster must implement.
+class VisitedLinkDelegate {
+ public:
+  // Returns true when the two BrowserContexts are equivalent.
+  virtual bool AreEquivalentContexts(content::BrowserContext* context1,
+                                     content::BrowserContext* context2) = 0;
+
+  // See RebuildTable.
+  class URLEnumerator {
+   public:
+    // Call this with each URL to rebuild the table.
+    virtual void OnURL(const GURL& url) = 0;
+
+    // This must be called by Delegate after RebuildTable is called. |success|
+    // indicates all URLs have been returned successfully.
+    virtual void OnComplete(bool success) = 0;
+
+   protected:
+    virtual ~URLEnumerator() {}
+  };
+
+  // Delegate class is responsible for persisting the list of visited URLs
+  // across browser runs. This is called by VisitedLinkMaster to repopulate
+  // its internal table.
+  virtual void RebuildTable(URLEnumerator* enumerator) = 0;

[joth, 2012/12/30 21:51:07]

Just realized, the History implementation of this delegates it onto
HistoryBackend to do at some point in future. (On same or another thread? Can't
easily see)
so we need to document that |enumerator| remains valid to be called after this
method returned. (And only on this thread? or on any thread?) And until when?
Until the next call to this method or the underlying VisitedLinkMaster is
destroyed? (guesses)

[boliu, 2013/01/02 17:09:36]

Yes, history calls enumerators on the background thread. Added documentation
that methods can be called on any thread, but the delegate is responsible for
synchronization.

+
+ protected:
+  virtual ~VisitedLinkDelegate() {}
+};
+
+#endif  // CHROME_BROWSER_VISITEDLINK_VISITEDLINK_DELEGATE_H_