Do not precache when the cache size is small

components/precache/content/precache_manager.h

Index: components/precache/content/precache_manager.h
diff --git a/components/precache/content/precache_manager.h b/components/precache/content/precache_manager.h
index e6bcc8094ab5e9a9bd5abed331d49c997cb20e85..621868ff9cd8381b22211a79c2295054cc1c806a 100644
--- a/components/precache/content/precache_manager.h
+++ b/components/precache/content/precache_manager.h
@@ -21,6 +21,7 @@
 #include "components/history/core/browser/history_types.h"
 #include "components/keyed_service/core/keyed_service.h"
 #include "components/precache/core/precache_fetcher.h"
+#include "net/disk_cache/disk_cache.h"
 #include "url/gurl.h"
 
 namespace base {
@@ -53,6 +54,9 @@ class PrecacheUnfinishedWork;
 // Visible for test.
 size_t NumTopHosts();
 
+// Minimum required cache size (inclusive).
+constexpr int kMinCacheSizeBytes = 40e6;

[twifkak, 2016/11/17 21:52:04]

FYI 40e6 is a float literal, which (by way of the constexpr) is getting cast at
compile time to an int. In this case, 40e6 is precise, so it works out. It feels
weird, but 53 bits ought to be enough for anybody, so I think it's fine.

[jamartin, 2016/11/18 03:55:32]

Acknowledged.

+
 // Class that manages all precaching-related activities. Owned by the
 // BrowserContext that it is constructed for. Use
 // PrecacheManagerFactory::GetForBrowserContext to get an instance of this
@@ -129,6 +133,10 @@ class PrecacheManager : public KeyedService,
   FRIEND_TEST_ALL_PREFIXES(PrecacheManagerTest, RecordStatsForFetchWithNonHTTP);
   FRIEND_TEST_ALL_PREFIXES(PrecacheManagerTest,
                            RecordStatsForFetchWithSizeZero);
+  FRIEND_TEST_ALL_PREFIXES(PrecacheManagerTest,
+                           StartPrecachingStopsOnSmallCaches);
+  FRIEND_TEST_ALL_PREFIXES(PrecacheManagerTest,
+                           StartPrecachingWithGoodSizedCache);
 
   enum class AllowedType {
     ALLOWED,
@@ -156,6 +164,12 @@ class PrecacheManager : public KeyedService,
   // gets the list of TopHosts for metrics purposes, but otherwise does nothing.
   void OnHostsReceivedThenDone(const history::TopHostsList& host_counts);
 
+  void OnCacheBackendReceived(int net_error_code);

[twifkak, 2016/11/17 21:52:04]

Add function doc.

[jamartin, 2016/11/18 03:55:32]

Done.

+
+  // Cache size is required to figure out whether on not we can proceed with
+  // StartPrecaching.
+  void OnCacheSizeReceived(int cache_size_bytes);
+
   // Returns true if precaching is allowed for the browser context.
   AllowedType PrecachingAllowed() const;
 
@@ -203,6 +217,14 @@ class PrecacheManager : public KeyedService,
   // Flag indicating whether or not precaching is currently in progress.
   bool is_precaching_;
 
+  // Pointer to the backend of the HTTP cache. Used to get the current cache
+  // size. It is not owned and is reset on demand via callbacks.
+  disk_cache::Backend* cache_backend_;
+
+  // The minimum cache size allowed for precaching. We allow this to be modified
+  // for testing purposes.
+  int min_cache_size_bytes_ = kMinCacheSizeBytes;
+
   // Work that hasn't yet finished.
   std::unique_ptr<PrecacheUnfinishedWork> unfinished_work_;