Create a PrefStore in support of Blimp metrics collection.

blimp/engine/BUILD.gn

Index: blimp/engine/BUILD.gn
diff --git a/blimp/engine/BUILD.gn b/blimp/engine/BUILD.gn
index fda282ba94215c4ed08b7199554bf76cba585a45..fb6dd27f7d79592dcb741c57b640a122daac90d2 100644
--- a/blimp/engine/BUILD.gn
+++ b/blimp/engine/BUILD.gn
@@ -123,10 +123,13 @@ source_set("common") {
     "common/blimp_browser_context.h",
     "common/blimp_content_client.cc",
     "common/blimp_content_client.h",
+    "common/blimp_pref_store.cc",
+    "common/blimp_pref_store.h",
   ]
 
   deps = [
     "//base",
+    "//components/prefs",
     "//components/version_info",
     "//content/public/common",
     "//ui/base",
@@ -224,6 +227,24 @@ source_set("app_unit_tests") {
   ]
 }
 
+source_set("common_unit_tests") {
+  testonly = true
+
+  sources = [
+    "common/blimp_pref_store_unittest.cc",
+  ]
+
+  deps = [
+    ":common",
+    "//base",
+    "//base/test:run_all_unittests",
+    "//base/test:test_support",
+    "//components/prefs:test_support",
+    "//testing/gmock",
+    "//testing/gtest",
+  ]
+}
+
 source_set("feature_unit_tests") {
   testonly = true
 
@@ -249,6 +270,7 @@ source_set("unit_tests") {
 
   deps = [
     ":app_unit_tests",
+    ":common_unit_tests",
     ":feature_unit_tests",
   ]
 }