Move plugins to "sonar/desktop/plugins"

Summary:
Plugins moved from "sonar/desktop/src/plugins" to "sonar/desktop/plugins".

Fixed all the paths after moving.

New "desktop" folder structure:
- `src` - Flipper desktop app JS code executing in Electron Renderer (Chrome) process.
- `static` - Flipper desktop app JS code executing in Electron Main (Node.js) process.
- `plugins` - Flipper desktop JS plugins.
- `pkg` - Flipper packaging lib and CLI tool.
- `doctor` - Flipper diagnostics lib and CLI tool.
- `scripts` - Build scripts for Flipper desktop app.
- `headless` - Headless version of Flipper desktop app.
- `headless-tests` - Integration tests running agains Flipper headless version.

Reviewed By: mweststrate

Differential Revision: D20344186

fbshipit-source-id: d020da970b2ea1e001f9061a8782bfeb54e31ba0

desktop/plugins/fresco/ImagePool.tsx

@@ -0,0 +1,78 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @format
+ */
+
+import {ImageId, ImageData} from './api';
+
+export type ImagesMap = {[imageId in ImageId]: ImageData};
+
+const maxInflightRequests = 10;
+
+export default class ImagePool {
+  cache: ImagesMap = {};
+  requested: {[imageId in ImageId]: boolean} = {};
+  queued: Array<ImageId> = [];
+  inFlightRequests: number = 0;
+  fetchImage: (imageId: ImageId) => void;
+  updateNotificationScheduled: boolean = false;
+  onPoolUpdated: (images: ImagesMap) => void;
+
+  constructor(
+    fetchImage: (imageId: ImageId) => void,
+    onPoolUpdated: (images: ImagesMap) => void,
+  ) {
+    this.fetchImage = fetchImage;
+    this.onPoolUpdated = onPoolUpdated;
+  }
+
+  getImages(): ImagesMap {
+    return {...this.cache};
+  }
+
+  fetchImages(ids: Array<string>) {
+    for (const id of ids) {
+      if (!this.cache[id] && !this.requested[id]) {
+        this.requested[id] = true;
+
+        if (this.inFlightRequests < maxInflightRequests) {
+          this.inFlightRequests++;
+          this.fetchImage(id);
+        } else {
+          this.queued.unshift(id);
+        }
+      }
+    }
+  }
+
+  clear() {
+    this.cache = {};
+    this.requested = {};
+  }
+
+  _fetchCompleted(image: ImageData): void {
+    this.cache[image.imageId] = image;
+    delete this.requested[image.imageId];
+
+    if (this.queued.length > 0) {
+      const popped = this.queued.pop() as string;
+      this.fetchImage(popped);
+    } else {
+      this.inFlightRequests--;
+    }
+
+    if (!this.updateNotificationScheduled) {
+      this.updateNotificationScheduled = true;
+      window.setTimeout(this._notify, 1000);
+    }
+  }
+
+  _notify = () => {
+    this.updateNotificationScheduled = false;
+    this.onPoolUpdated(this.getImages());
+  };
+}