predictors: Refactor resource_prefetch_predictor_tables.

chrome/browser/predictors/resource_prefetch_predictor.proto

Index: chrome/browser/predictors/resource_prefetch_predictor.proto
diff --git a/chrome/browser/predictors/resource_prefetch_predictor.proto b/chrome/browser/predictors/resource_prefetch_predictor.proto
index 6d2a59be1a5bf56905c926b4bb44a4ef367e4a11..023b27d93878bb594fe49c7b5d2fad1668cc980c 100644
--- a/chrome/browser/predictors/resource_prefetch_predictor.proto
+++ b/chrome/browser/predictors/resource_prefetch_predictor.proto
@@ -13,11 +13,7 @@ package predictors;
 // Required in Chrome.
 option optimize_for = LITE_RUNTIME;
 
-message Metadata {
-  optional string main_page_url = 1;
-  optional uint64 last_visit_time = 2;
-}
-
+// Represents a single subresource.
 message ResourceData {
   // Mirrors content::ResourceType.
   enum ResourceType {
@@ -62,6 +58,14 @@ message ResourceData {
   optional bool always_revalidate = 9;
 }
 
+// Represents a collection of subresources associated with URL or host.
+message PrefetchData {
+  // Main frame URL of host.
+  optional string primary_key = 1;
+  optional uint64 last_visit_time = 2;
+  repeated ResourceData resources = 3;
+}
+
 // Represents a mapping from URL or host to a list of redirect endpoints.
 message RedirectData {
   // Represents a single redirect chain endpoint.
@@ -73,7 +77,7 @@ message RedirectData {
     optional uint32 consecutive_misses = 4;
   }
 
-  // Represents main frame URL or host.
+  // Main frame URL or host.
   optional string primary_key = 1;
   optional uint64 last_visit_time = 2;
   repeated RedirectStat redirect_endpoints = 3;