Convert JsonWriter::Write to taking a const ref for the in-param

Clearer API; flushes out a lot of unnecessary heap allocations.

depends on https://codereview.chromium.org/1129083003/

BUG=none

Review URL: https://codereview.chromium.org/1131113004

Cr-Commit-Position: refs/heads/master@{#330255}
diff --git a/components/proximity_auth/client.cc b/components/proximity_auth/client.cc
index a0b6a06..255b6f6 100644
--- a/components/proximity_auth/client.cc
+++ b/components/proximity_auth/client.cc
@@ -37,7 +37,7 @@
 // Serializes the |value| to a JSON string and returns the result.
 std::string SerializeValueToJson(const base::Value& value) {
   std::string json;
-  base::JSONWriter::Write(&value, &json);
+  base::JSONWriter::Write(value, &json);
   return json;
 }