refactor: use v8 serialization for ipc (#20214)

* refactor: use v8 serialization for ipc

* cloning process.env doesn't work

* serialize host objects by enumerating key/values

* new serialization can handle NaN, Infinity, and undefined correctly

* can't allocate v8 objects during GC

* backport microtasks fix

* fix compile

* fix node_stream_loader reentrancy

* update subframe spec to expect undefined instead of null

* write undefined instead of crashing when serializing host objects

* fix webview spec

* fix download spec

* buffers are transformed into uint8arrays

* can't serialize promises

* fix chrome.i18n.getMessage

* fix devtools tests

* fix zoom test

* fix debug build

* fix lint

* update ipcRenderer tests

* fix printToPDF test

* update patch

* remove accidentally re-added remote-side spec

* wip

* don't attempt to serialize host objects

* jump through different hoops to set options.webContents sometimes

* whoops

* fix lint

* clean up error-handling logic

* fix memory leak

* fix lint

* convert host objects using old base::Value serialization

* fix lint more

* fall back to base::Value-based serialization

* remove commented-out code

* add docs to breaking-changes.md

* Update breaking-changes.md

* update ipcRenderer and WebContents docs

* lint

* use named values for format tag

* save a memcpy for ~30% speedup

* get rid of calls to ShallowClone

* extra debugging for paranoia

* d'oh, use the correct named tags

* apparently msstl doesn't like this DCHECK

* funny story about that DCHECK

* disable remote-related functions when enable_remote_module = false

* nits

* use EnableIf to disable remote methods in mojom

* fix include

* review comments

docs/api/breaking-changes.md

@@ -6,6 +6,59 @@ Breaking changes will be documented here, and deprecation warnings added to JS c
 
 The `FIXME` string is used in code comments to denote things that should be fixed for future releases. See https://github.com/electron/electron/search?q=fixme
 
+## Planned Breaking API Changes (8.0)
+
+### Values sent over IPC are now serialized with Structured Clone Algorithm
+
+The algorithm used to serialize objects sent over IPC (through
+`ipcRenderer.send`, `ipcRenderer.sendSync`, `WebContents.send` and related
+methods) has been switched from a custom algorithm to V8's built-in [Structured
+Clone Algorithm][SCA], the same algorithm used to serialize messages for
+`postMessage`. This brings about a 2x performance improvement for large
+messages, but also brings some breaking changes in behavior.
+
+- Sending Functions, Promises, WeakMaps, WeakSets, or objects containing any
+  such values, over IPC will now throw an exception, instead of silently
+  converting the functions to `undefined`.
+```js
+// Previously:
+ipcRenderer.send('channel', { value: 3, someFunction: () => {} })
+// => results in { value: 3 } arriving in the main process
+
+// From Electron 8:
+ipcRenderer.send('channel', { value: 3, someFunction: () => {} })
+// => throws Error("() => {} could not be cloned.")
+```
+- `NaN`, `Infinity` and `-Infinity` will now be correctly serialized, instead
+  of being converted to `null`.
+- Objects containing cyclic references will now be correctly serialized,
+  instead of being converted to `null`.
+- `Set`, `Map`, `Error` and `RegExp` values will be correctly serialized,
+  instead of being converted to `{}`.
+- `BigInt` values will be correctly serialized, instead of being converted to
+  `null`.
+- Sparse arrays will be serialized as such, instead of being converted to dense
+  arrays with `null`s.
+- `Date` objects will be transferred as `Date` objects, instead of being
+  converted to their ISO string representation.
+- Typed Arrays (such as `Uint8Array`, `Uint16Array`, `Uint32Array` and so on)
+  will be transferred as such, instead of being converted to Node.js `Buffer`.
+- Node.js `Buffer` objects will be transferred as `Uint8Array`s. You can
+  convert a `Uint8Array` back to a Node.js `Buffer` by wrapping the underlying
+  `ArrayBuffer`:
+```js
+Buffer.from(value.buffer, value.byteOffset, value.byteLength)
+```
+
+Sending any objects that aren't native JS types, such as DOM objects (e.g.
+`Element`, `Location`, `DOMMatrix`), Node.js objects (e.g. `process.env`,
+`Stream`), or Electron objects (e.g. `WebContents`, `BrowserWindow`,
+`WebFrame`) is deprecated. In Electron 8, these objects will be serialized as
+before with a DeprecationWarning message, but starting in Electron 9, sending
+these kinds of objects will throw a 'could not be cloned' error.
+
+[SCA]: https://developer.mozilla.org/en-US/docs/Web/API/Web_Workers_API/Structured_clone_algorithm
+
 ## Planned Breaking API Changes (7.0)
 
 ### Node Headers URL