predictors: Remove unused field from the resource_prefetch_predictor database.

chrome/browser/predictors/resource_prefetch_predictor_tables.h

Index: chrome/browser/predictors/resource_prefetch_predictor_tables.h
diff --git a/chrome/browser/predictors/resource_prefetch_predictor_tables.h b/chrome/browser/predictors/resource_prefetch_predictor_tables.h
index a089544274e6e1adb21e7fa1eef17e917b605a6b..bdb14fe9397653cfd6e299ddf90b5ac306a91168 100644
--- a/chrome/browser/predictors/resource_prefetch_predictor_tables.h
+++ b/chrome/browser/predictors/resource_prefetch_predictor_tables.h
@@ -44,8 +44,7 @@ class ResourcePrefetchPredictorTables : public PredictorTableBase {
   struct ResourceRow {
     ResourceRow();
     ResourceRow(const ResourceRow& other);
-    ResourceRow(const std::string& main_frame_url,
-                const std::string& resource_url,
+    ResourceRow(const std::string& resource_url,
                 content::ResourceType resource_type,
                 int number_of_hits,
                 int number_of_misses,
@@ -59,11 +58,6 @@ class ResourcePrefetchPredictorTables : public PredictorTableBase {
     static void FromProto(const ResourceData& proto, ResourceRow* row);
     void ToProto(ResourceData* resource_data) const;
 
-    // Stores the host for host based data, main frame Url for the Url based
-    // data. This field is cleared for efficiency reasons and the code outside
-    // this class should not assume it is set.
-    std::string primary_key;
-
     GURL resource_url;
     content::ResourceType resource_type;
     size_t number_of_hits;

[pasko, 2016/08/26 13:40:30]

Do we want to still plumb these one by one in FromProto/ToProto? Is removing
them a plan for the next cleanup?

[Benoit L, 2016/08/29 13:11:39]

If the proto doesn't reflect everything and needs methods added, no.

@@ -126,7 +120,7 @@ class ResourcePrefetchPredictorTables : public PredictorTableBase {
   virtual void DeleteAllData();
 
   // The maximum length of the string that can be stored in the DB.
-  static const size_t kMaxStringLength;
+  static const size_t kMaxStringLength = 1024;

[pasko, 2016/08/26 13:40:30]

I would recommend constexpr. The idea of including this constant in all the
various .cc files and then resolving the duplicates in the linker is not
uncommon in C++ land, but somehow feels less optimal, given a strictly better
alternative. 

[Benoit L, 2016/08/29 13:11:39]

Done.

 
  private:
   friend class PredictorDatabaseInternal;
@@ -146,7 +140,7 @@ class ResourcePrefetchPredictorTables : public PredictorTableBase {
 
   // Returns true if the strings in the |data| are less than |kMaxStringLength|
   // in length.
-  bool StringsAreSmallerThanDBLimit(const PrefetchData& data) const;
+  static bool StringsAreSmallerThanDBLimit(const PrefetchData& data);
 
   // PredictorTableBase methods.
   void CreateTableIfNonExistent() override;