ntp_tiles::metrics: Add rappor metrics for impression URLs per icon type.

components/ntp_tiles/metrics.h

Index: components/ntp_tiles/metrics.h
diff --git a/components/ntp_tiles/metrics.h b/components/ntp_tiles/metrics.h
index c32dbf258df3a21c54958841bd61274cf2120c98..009c4942b8be62d4b58e6d3aff742e6ad66a26f2 100644
--- a/components/ntp_tiles/metrics.h
+++ b/components/ntp_tiles/metrics.h
@@ -9,6 +9,11 @@
 #include <vector>
 
 #include "components/ntp_tiles/ntp_tile.h"
+#include "url/gurl.h"
+
+namespace rappor {
+class RapporService;
+}  // namespace rappor
 
 namespace ntp_tiles {
 namespace metrics {
@@ -39,10 +44,22 @@ enum MostVisitedTileType {
   UNKNOWN_TILE_TYPE,
 };
 
+struct TileImpression {
+  TileImpression(NTPTileSource source,
+                 MostVisitedTileType type,
+                 const GURL& url)
+      : source(source), type(type), url(url) {}
+
+  NTPTileSource source;
+  MostVisitedTileType type;
+  GURL url;
+};
+
 // Records an NTP impression, after all tiles have loaded.
-// Includes the visual types (see above) of all visible tiles.
-void RecordPageImpression(
-    const std::vector<std::pair<NTPTileSource, MostVisitedTileType>>& tiles);
+// Includes the visual types (see above) of all visible tiles. If
+// |rappor_service| is null, no rappor metrics will be reported.
+void RecordPageImpression(const std::vector<TileImpression>& tiles,
+                          rappor::RapporService* rappor_service);
 
 // Records a click on a tile.
 void RecordTileClick(int index,