Expose a send method with a string params

Summary:
For C++, folly::dynamic is used throughout.

On iOS and Android though, Flipper goes through multiple conversions to get to a folly::dynamic only to ultimately obtain a JSON string from it.

Let's take a look at Android:

There are multiple types like FlipperObject, FlipperArray that wrap around a JSONObject.

When data needs to be sent:
1. The JSONObject is asked for its string representation.
2. The string representation is then parsed by folly to construct the folly::dynamic instance.
3. The step above involves an extra boundary cross through JNI.
4. Ultimately, a socket or ws connection does not understand folly::dynamic so we then get a JSON string representation from it.
5. Data is sent.

As described above, for big enough objects, this represents an issue.

So, the idea of this change, is to allow plugins to send a JSON string instead. This will remove a few serialisation/deserialisation steps from the process.

*Note: this API is not currently used by anything so there's no impact to existing plugins.*

Changelog: expose a send method that accept a string as params

Reviewed By: LukeDefeo

Differential Revision: D38741582

fbshipit-source-id: 78e0acd80fc8c97378ee986cbaf377078996ed60

xplat/FlipperTestLib/FlipperConnectionManagerMock.h

@@ -40,6 +40,10 @@ class FlipperConnectionManagerMock : public FlipperConnectionManager {
     messages.push_back(message);
   }
 
+  void sendMessage(const std::string& message) override {
+    messages.push_back(folly::parseJson(message));
+  }
+
   void setCertificateProvider(
       const std::shared_ptr<FlipperCertificateProvider> provider) override{};
 

xplat/FlipperTestLib/FlipperConnectionMock.h

@@ -8,6 +8,7 @@
 #pragma once
 
 #include <Flipper/FlipperConnection.h>
+#include <folly/json.h>
 #include <map>
 #include <queue>
 #include <string>
@@ -22,6 +23,11 @@ class FlipperConnectionMock : public FlipperConnection {
     sent_message_history[method].push(params);
   }
 
+  void send(const std::string& method, const std::string& params) override {
+    sent_[method] = folly::parseJson(params);
+    sent_message_history[method].push(params);
+  }
+
   void receive(const std::string& method, const FlipperReceiver& receiver)
       override {
     receivers_[method] = receiver;