Add pause/resume functionality to precache

components/precache/core/BUILD.gn

Index: components/precache/core/BUILD.gn
diff --git a/components/precache/core/BUILD.gn b/components/precache/core/BUILD.gn
index 5aa770878762536b190108dc19512360b4fa7e9e..bc0fbdcbb865eed3ab6ae725a11cc1b6a97ec9b6 100644
--- a/components/precache/core/BUILD.gn
+++ b/components/precache/core/BUILD.gn
@@ -25,6 +25,8 @@ source_set("core") {
     "precache_database.h",
     "precache_fetcher.cc",
     "precache_fetcher.h",
+    "precache_session_table.cc",
+    "precache_session_table.h",
     "precache_switches.cc",
     "precache_switches.h",
     "precache_url_table.cc",
@@ -50,6 +52,7 @@ source_set("core") {
 proto_library("proto") {
   sources = [
     "proto/precache.proto",
+    "proto/unfinished_work.proto",
   ]
 }
 
@@ -59,6 +62,7 @@ source_set("unit_tests") {
     "fetcher_pool_unittest.cc",
     "precache_database_unittest.cc",
     "precache_fetcher_unittest.cc",
+    "precache_session_table_unittest.cc",
     "precache_url_table_unittest.cc",
   ]