Fix GN build for components/session_manager and /chromeos

BUG=None
TEST=user_manager GN ninja build (debug|official; is_component_build=yes|no)
TBR=oshima

Review URL: https://codereview.chromium.org/880203003

Cr-Commit-Position: refs/heads/master@{#313479}

chromeos/BUILD.gn

@@ -28,6 +28,7 @@ component("chromeos") {
     "//components/policy/proto",
     "//components/onc",
     "//crypto",
+    "//crypto:platform",
     "//google_apis",
     "//net/third_party/nss/ssl:libssl",
     "//third_party/icu",

components/session_manager/core/BUILD.gn

@@ -8,5 +8,11 @@ component("core") {
     "session_manager.cc",
     "session_manager.h",
   ]
+  deps = [
+    "//base",
+  ]
+  if (is_chromeos) {
+    deps += [ "//chromeos" ]
+  }
   defines = [ "SESSION_IMPLEMENTATION" ]
 }