Precache: Optionally rank resources-to-precache globally.

components/precache/core/proto/unfinished_work.proto

Index: components/precache/core/proto/unfinished_work.proto
diff --git a/components/precache/core/proto/unfinished_work.proto b/components/precache/core/proto/unfinished_work.proto
index 700db23dfdc0d287188b0c485dd8f1310e614b1d..67c5eb042c5a5b28a82ad98038855c1269f52e27 100644
--- a/components/precache/core/proto/unfinished_work.proto
+++ b/components/precache/core/proto/unfinished_work.proto
@@ -14,6 +14,9 @@ option optimize_for = LITE_RUNTIME;
 message TopHost {
   // The host name of a top host.
   optional string hostname = 1;
+
+  // The number of visits it had by this user.
+  optional int64 visits = 2;
 };
 
 // Information about the precache work that needs to be completed.
@@ -43,8 +46,12 @@ message PrecacheUnfinishedWork {
   // The total number of manifest URLs that the precache session started with.
   optional uint64 num_manifest_urls = 7;
 
+  // The total number of resource URLs that the precache session gathered from
+  // the manifests.
+  optional uint64 num_resource_urls = 9;
+
   // The internal value of a base::Time object representing the precache
   // session start time. The start time is the time just before when top hosts
   // are requested.
   optional int64 start_time = 8;
-};
+};