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

spec/api-browser-window-spec.js

@@ -1381,24 +1381,25 @@ describe('BrowserWindow module', () => {
         })
         let htmlPath = path.join(fixtures, 'api', 'sandbox.html?verify-ipc-sender')
         const pageUrl = 'file://' + htmlPath
-        w.loadURL(pageUrl)
+        let childWc
         w.webContents.once('new-window', (e, url, frameName, disposition, options) => {
-          let parentWc = w.webContents
-          let childWc = options.webContents
-          assert.notEqual(parentWc, childWc)
-          ipcMain.once('parent-ready', function (event) {
-            assert.equal(parentWc, event.sender)
-            parentWc.send('verified')
-          })
-          ipcMain.once('child-ready', function (event) {
-            assert.equal(childWc, event.sender)
-            childWc.send('verified')
-          })
-          waitForEvents(ipcMain, [
-            'parent-answer',
-            'child-answer'
-          ], done)
+          childWc = options.webContents
+          assert.notEqual(w.webContents, childWc)
         })
+        ipcMain.once('parent-ready', function (event) {
+          assert.equal(w.webContents, event.sender)
+          event.sender.send('verified')
+        })
+        ipcMain.once('child-ready', function (event) {
+          assert(childWc)
+          assert.equal(childWc, event.sender)
+          event.sender.send('verified')
+        })
+        waitForEvents(ipcMain, [
+          'parent-answer',
+          'child-answer'
+        ], done)
+        w.loadURL(pageUrl)
       })
 
       describe('event handling', () => {