Apply idle optimizations throughout code base

Summary:
See explanation in parent diff, make sure the idler is used efficiently, instead of wasting a lot of CPU creating a new callstack every time `idle` is called.

Also fixed that cancelled idlers could result in an _uncaught_ exception

Reviewed By: nikoant

Differential Revision: D19158593

fbshipit-source-id: 0be505a74c374e0ca6ee0e79b1f1e98ac9b80467

src/utils/Idler.tsx

@@ -25,7 +25,7 @@ export class Idler implements BaseIdler {
     return this.kill || performance.now() - this.lastIdle > this.interval;
   }
 
-  idle(): Promise<void> {
+  async idle(): Promise<void> {
     if (this.kill) {
       throw new CancelledPromiseError('Idler got killed');
     }
@@ -34,7 +34,7 @@ export class Idler implements BaseIdler {
       this.lastIdle = now;
       return new Promise(resolve => setTimeout(resolve, 0));
     }
-    return Promise.resolve();
+    return undefined;
   }
 
   cancel() {

src/utils/serialization.tsx

@@ -136,7 +136,7 @@ export async function makeObjectSerializable(
   let prevStackLength = stack.length;
   let accumulator = prevStackLength;
   while (stack.length > 0) {
-    if (idler) {
+    if (idler && idler.shouldIdle()) {
       await idler.idle();
     }
     const element = stack[stack.length - 1];