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diff --git a/chrome/browser/renderer_host/web_cache_manager.h b/chrome/browser/renderer_host/web_cache_manager.h
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+// Copyright (c) 2006-2008 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.
+
+// This is the browser side of the cache manager, it tracks the activity of the
+// render processes and allocates available memory cache resources.
+
+#ifndef CHROME_BROWSER_WEB_CACHE_MANAGER_H_
+#define CHROME_BROWSER_WEB_CACHE_MANAGER_H_
+
+#include <map>
+#include <list>
+#include <set>
+
+#include "base/basictypes.h"
+#include "base/shared_memory.h"
+#include "base/singleton.h"
+#include "base/task.h"
+#include "base/time.h"
+#include "third_party/WebKit/WebKit/chromium/public/WebCache.h"
+
+class PrefService;
+
+class WebCacheManager {
+  // Unit tests are our friends.
+  friend class WebCacheManagerTest;
+
+ public:
+  static void RegisterPrefs(PrefService* prefs);
+
+  // Gets the singleton WebCacheManager object.  The first time this method
+  // is called, a WebCacheManager object is constructed and returned.
+  // Subsequent calls will return the same object.
+  static WebCacheManager* GetInstance();
+
+  // When a render process is created, it registers itself with the cache
+  // manager host, causing the renderer to be allocated cache resources.
+  void Add(int renderer_id);
+
+  // When a render process ends, it removes itself from the cache manager host,
+  // freeing the manager to assign its cache resources to other renderers.
+  void Remove(int renderer_id);
+
+  // The cache manager assigns more cache resources to active renderer.  When a
+  // renderer is active, it should inform the cache manager to receive more
+  // cache resources.
+  //
+  // When a renderer moves from being inactive to being active, the cache
+  // manager may decide to adjust its resource allocation, but it will delay
+  // the recalculation, allowing ObserveActivity to return quickly.
+  void ObserveActivity(int renderer_id);
+
+  // Periodically, renderers should inform the cache manager of their current
+  // statistics.  The more up-to-date the cache manager's statistics, the
+  // better it can allocate cache resources.
+  void ObserveStats(
+      int renderer_id, const WebKit::WebCache::UsageStats& stats);
+
+  // The global limit on the number of bytes in all the in-memory caches.
+  size_t global_size_limit() const { return global_size_limit_; }
+
+  // Sets the global size limit, forcing a recalculation of cache allocations.
+  void SetGlobalSizeLimit(size_t bytes);
+
+  // Gets the default global size limit.  This interrogates system metrics to
+  // tune the default size to the current system.
+  static size_t GetDefaultGlobalSizeLimit();
+
+ protected:
+  // The amount of idle time before we consider a tab to be "inactive"
+  static const int kRendererInactiveThresholdMinutes = 5;
+
+  // Keep track of some renderer information.
+  struct RendererInfo : WebKit::WebCache::UsageStats {
+    // The access time for this renderer.
+    base::Time access;
+  };
+
+  typedef std::map<int, RendererInfo> StatsMap;
+
+  // An allocation is the number of bytes a specific renderer should use for
+  // its cache.
+  typedef std::pair<int,size_t> Allocation;
+
+  // An allocation strategy is a list of allocations specifying the resources
+  // each renderer is permitted to consume for its cache.
+  typedef std::list<Allocation> AllocationStrategy;
+
+  // This class is a singleton.  Do not instantiate directly.
+  WebCacheManager();
+  friend struct DefaultSingletonTraits<WebCacheManager>;
+
+  ~WebCacheManager();
+
+  // Recomputes the allocation of cache resources among the renderers.  Also
+  // informs the renderers of their new allocation.
+  void ReviseAllocationStrategy();
+
+  // Schedules a call to ReviseAllocationStrategy after a short delay.
+  void ReviseAllocationStrategyLater();
+
+  // The various tactics used as part of an allocation strategy.  To decide
+  // how many resources a given renderer should be allocated, we consider its
+  // usage statistics.  Each tactic specifies the function that maps usage
+  // statistics to resource allocations.
+  //
+  // Determining a resource allocation strategy amounts to picking a tactic
+  // for each renderer and checking that the total memory required fits within
+  // our |global_size_limit_|.
+  enum AllocationTactic {
+    // Ignore cache statistics and divide resources equally among the given
+    // set of caches.
+    DIVIDE_EVENLY,
+
+    // Allow each renderer to keep its current set of cached resources, with
+    // some extra allocation to store new objects.
+    KEEP_CURRENT_WITH_HEADROOM,
+
+    // Allow each renderer to keep its current set of cached resources.
+    KEEP_CURRENT,
+
+    // Allow each renderer to keep cache resources it believs are currently
+    // being used, with some extra allocation to store new objects.
+    KEEP_LIVE_WITH_HEADROOM,
+
+    // Allow each renderer to keep cache resources it believes are currently
+    // being used, but instruct the renderer to discard all other data.
+    KEEP_LIVE,
+  };
+
+  // Helper functions for devising an allocation strategy
+
+  // Add up all the stats from the given set of renderers and place the result
+  // in |stats|.
+  void GatherStats(const std::set<int>& renderers,
+                   WebKit::WebCache::UsageStats* stats);
+
+  // Get the amount of memory that would be required to implement |tactic|
+  // using the specified allocation tactic.  This function defines the
+  // semantics for each of the tactics.
+  static size_t GetSize(AllocationTactic tactic,
+                        const WebKit::WebCache::UsageStats& stats);
+
+  // Attempt to use the specified tactics to compute an allocation strategy
+  // and place the result in |strategy|.  |active_stats| and |inactive_stats|
+  // are the aggregate statistics for |active_renderers_| and
+  // |inactive_renderers_|, respectively.
+  //
+  // Returns |true| on success and |false| on failure.  Does not modify
+  // |strategy| on failure.
+  bool AttemptTactic(AllocationTactic active_tactic,
+                     const WebKit::WebCache::UsageStats& active_stats,
+                     AllocationTactic inactive_tactic,
+                     const WebKit::WebCache::UsageStats& inactive_stats,
+                     AllocationStrategy* strategy);
+
+  // For each renderer in |renderers|, computes its allocation according to
+  // |tactic| and add the result to |strategy|.  Any |extra_bytes_to_allocate|
+  // is divided evenly among the renderers.
+  void AddToStrategy(std::set<int> renderers,
+                     AllocationTactic tactic,
+                     size_t extra_bytes_to_allocate,
+                     AllocationStrategy* strategy);
+
+  // Enact an allocation strategy by informing the renderers of their
+  // allocations according to |strategy|.
+  void EnactStrategy(const AllocationStrategy& strategy);
+
+  // Check to see if any active renderers have fallen inactive.
+  void FindInactiveRenderers();
+
+  // The global size limit for all in-memory caches.
+  size_t global_size_limit_;
+
+  // Maps every renderer_id our most recent copy of its statistics.
+  StatsMap stats_;
+
+  // Every renderer we think is still around is in one of these two sets.
+  //
+  // Active renderers are those renderers that have been active more recently
+  // than they have been inactive.
+  std::set<int> active_renderers_;
+  // Inactive renderers are those renderers that have been inactive more
+  // recently than they have been active.
+  std::set<int> inactive_renderers_;
+
+  ScopedRunnableMethodFactory<WebCacheManager> revise_allocation_factory_;
+
+  DISALLOW_COPY_AND_ASSIGN(WebCacheManager);
+};
+
+#endif  // CHROME_BROWSER_WEB_CACHE_MANAGER_H_