Add PrerenderLocalPredictor, which will eventually perform

chrome/browser/prerender/prerender_local_predictor.cc

Index: chrome/browser/prerender/prerender_local_predictor.cc
===================================================================
--- chrome/browser/prerender/prerender_local_predictor.cc	(revision 0)
+++ chrome/browser/prerender/prerender_local_predictor.cc	(revision 0)
@@ -0,0 +1,136 @@
+// 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.
+
+#include "chrome/browser/prerender/prerender_local_predictor.h"
+
+#include "base/timer.h"
+#include "chrome/browser/prerender/prerender_manager.h"
+#include "chrome/browser/profiles/profile.h"
+#include "chrome/browser/history/history.h"
+#include "chrome/browser/history/history_database.h"
+#include "content/public/browser/browser_thread.h"
+
+using content::BrowserThread;
+
+namespace prerender {
+
+namespace {
+
+// Task to lookup the URL for a given URLID.
+class GetURLForURLIDTask : public HistoryDBTask {
+ public:
+  GetURLForURLIDTask(PrerenderLocalPredictor* local_predictor,
+                     history::URLID url_id)
+      : local_predictor_(local_predictor),
+        url_id_(url_id),
+        success_(false) {
+  }
+  virtual bool RunOnDBThread(history::HistoryBackend* backend,
+                             history::HistoryDatabase* db) {
+    history::URLRow url_row;
+    success_ = db->GetURLRow(url_id_, &url_row);
+    if (success_)
+      url_ = url_row.url();
+    return true;
+  }
+  virtual void DoneRunOnMainThread() {
+    if (success_)
+      local_predictor_->OnLookupURL(url_id_, url_);
+  }
+ private:
+  PrerenderLocalPredictor* local_predictor_;
+  history::URLID url_id_;
+  bool success_;
+  GURL url_;
+  DISALLOW_COPY_AND_ASSIGN(GetURLForURLIDTask);
+};
+
+// Task to load history from the visit database on startup.
+class GetVisitHistoryTask : public HistoryDBTask {
+ public:
+  GetVisitHistoryTask(PrerenderLocalPredictor* local_predictor,
+                      int max_visits)
+      : local_predictor_(local_predictor),
+        max_visits_(max_visits),
+        visit_history_(new std::vector<history::BriefVisitInfo>) {
+  }
+  virtual bool RunOnDBThread(history::HistoryBackend* backend,
+                             history::HistoryDatabase* db) {
+    db->GetBriefVisitInfoOfMostRecentVisits(max_visits_, visit_history_.get());
+    return true;
+  }
+  virtual void DoneRunOnMainThread() {
+    local_predictor_->OnGetInitialVisitHistory(visit_history_.release());
+  }
+ private:
+  PrerenderLocalPredictor* local_predictor_;
+  int max_visits_;
+  scoped_ptr<std::vector<history::BriefVisitInfo> > visit_history_;
+  DISALLOW_COPY_AND_ASSIGN(GetVisitHistoryTask);
+};
+
+};
+
+HistoryService* PrerenderLocalPredictor::GetHistoryIfExists() const {
+  Profile* profile = prerender_manager_->profile();
+  if (!profile)
+    return NULL;
+  return profile->GetHistoryServiceWithoutCreating();
+}
+
+PrerenderLocalPredictor::PrerenderLocalPredictor(
+    PrerenderManager* prerender_manager)
+    : prerender_manager_(prerender_manager),
+      visit_history_initialized_(false) {
+  if (MessageLoop::current()) {
+    timer_.Start(FROM_HERE,
+                 base::TimeDelta::FromMilliseconds(kInitDelayMs),
+                 this,
+                 &PrerenderLocalPredictor::Init);

[cbentzel, 2012/04/17 20:28:16]

Potential for a use-after-free here if the Predictor is deleted before the task
is handled. This could be a weak pointer supporting class.

[tburkard, 2012/04/17 20:51:36]

Shouldn't, because timer_ takes care of this (when destructed), I thought?
On 2012/04/17 20:28:16, cbentzel wrote:

[cbentzel, 2012/04/17 20:57:51]

Yeah, you are right. 

+  }
+}
+
+void PrerenderLocalPredictor::OnGetInitialVisitHistory(
+    std::vector<history::BriefVisitInfo>* visit_history) {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
+  DCHECK(!visit_history_initialized_);
+  visit_history_.reset(visit_history);
+  visit_history_initialized_ = true;
+}
+
+void PrerenderLocalPredictor::Init() {
+  HistoryService* history = GetHistoryIfExists();
+  if (!history) {
+    // TODO(tburkard): Record this somewhere (eg histogram) and/or try again
+    // later.
+    return;
+  }
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
+  history->ScheduleDBTask(
+      new GetVisitHistoryTask(this, kMaxVisitHistory),
+      &history_db_consumer_);
+  history->AddVisitDatabaseObserver(this);
+}
+
+void PrerenderLocalPredictor::OnAddVisit(history::BriefVisitInfo info) {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
+  HistoryService* history = GetHistoryIfExists();
+  if (history) {
+    history->ScheduleDBTask(
+        new GetURLForURLIDTask(this, info.url_id),

[cbentzel, 2012/04/17 20:28:16]

Why do you need to do this? I thought the whole purpose of adding the observer
to the VisitDB was to minimize URL table lookups? 

[tburkard, 2012/04/17 20:51:36]

I will eventually need to lookup URLs when I want to actually prerender.

As for why I'm doing it here, it was mostly to demonstrate the APIs I'm using. 
This is not really doing anything useful yet.  Once I make the second CL that is
actually using this info and initiating prerenders, this line will go away, and
the URL lookup will only occur at places where we actually need the URL.
On 2012/04/17 20:28:16, cbentzel wrote:

[cbentzel, 2012/04/17 20:57:51]

OK. I'd just remove it for now.

+        &history_db_consumer_);
+  }
+}
+
+PrerenderLocalPredictor::~PrerenderLocalPredictor() {
+  HistoryService* history = GetHistoryIfExists();
+  if (history)
+    history->RemoveVisitDatabaseObserver(this);
+}
+
+void PrerenderLocalPredictor::OnLookupURL(history::URLID url_id, GURL url) {
+
+}
+
+}  // namespace prerender