perf: don't use JSON to send the result of ipcRenderer.sendSync. (#8953)

* Don't use JSON to send the result of `ipcRenderer.sendSync`.

- Change the return type of AtomViewHostMsg_Message_Sync from `base::string16`
  to `base::ListValue`
- Adjust lib/browser/api/web-contents.js and /lib/renderer/api/ipc-renderer.js
  to wrap/unwrap return values to/from array, instead of
  serializing/deserializing JSON.

This change can greatly improve `ipcRenderer.sendSync` calls where the return
value contains Buffer instances, because those are converted to Array before
being serialized to JSON(which has no efficient way of representing byte
arrays).

A simple benchmark where remote.require('fs') was used to read a 16mb file got
at least 5x faster, not to mention it used a lot less memory.  This difference
tends increases with larger buffers.

* Don't base64 encode Buffers

* Don't allocate V8ValueConverter on the heap

* Replace hidden global.sandbox with NodeBindings::IsInitialized()

* Refactoring: check NodeBindings::IsInitialized() in V8ValueConverter

* Refactor problematic test to make it more reliable

* Add tests for NaN and Infinity

atom/common/native_mate_converters/v8_value_converter.h

@@ -24,7 +24,6 @@ class V8ValueConverter {
   void SetRegExpAllowed(bool val);
   void SetFunctionAllowed(bool val);
   void SetStripNullFromObjects(bool val);
-  void SetDisableNode(bool val);
   v8::Local<v8::Value> ToV8Value(const base::Value* value,
                                  v8::Local<v8::Context> context) const;
   base::Value* FromV8Value(v8::Local<v8::Value> value,
@@ -63,13 +62,6 @@ class V8ValueConverter {
   // If true, we will convert Function JavaScript objects to dictionaries.
   bool function_allowed_ = false;
 
-  // If true, will not use node::Buffer::Copy to deserialize byte arrays.
-  // node::Buffer::Copy depends on a working node.js environment, and this is
-  // not desirable in sandboxed renderers. That means Buffer instances sent from
-  // browser process will be deserialized as browserify-based Buffer(which are
-  // wrappers around Uint8Array).
-  bool disable_node_ = false;
-
   // If true, undefined and null values are ignored when converting v8 objects
   // into Values.
   bool strip_null_from_objects_ = false;