Bug 1467858 - Add site thumbnail, router html and bug fixes to Activity Stream. r=k88hudson

MozReview-Commit-ID: FCL0cGMubbY

browser/extensions/activity-stream/content-src/lib/screenshot-utils.js

@@ -0,0 +1,50 @@
+/**
+ * List of helper functions for screenshot-based images.
+ *
+ * There are two kinds of images:
+ * 1. Remote Image: This is the image from the main process and it refers to
+ *    the image in the React props. This can either be an object with the `data`
+ *    and `path` properties, if it is a blob, or a string, if it is a normal image.
+ * 2. Local Image: This is the image object in the content process and it refers
+ *    to the image *object* in the React component's state. All local image
+ *    objects have the `url` property, and an additional property `path`, if they
+ *    are blobs.
+ */
+export const ScreenshotUtils = {
+  isBlob(isLocal, image) {
+    return !!(image && image.path && ((!isLocal && image.data) || (isLocal && image.url)));
+  },
+
+  // This should always be called with a remote image and not a local image.
+  createLocalImageObject(remoteImage) {
+    if (!remoteImage) {
+      return null;
+    }
+    if (this.isBlob(false, remoteImage)) {
+      return {url: global.URL.createObjectURL(remoteImage.data), path: remoteImage.path};
+    }
+    return {url: remoteImage};
+  },
+
+  // Revokes the object URL of the image if the local image is a blob.
+  // This should always be called with a local image and not a remote image.
+  maybeRevokeBlobObjectURL(localImage) {
+    if (this.isBlob(true, localImage)) {
+      global.URL.revokeObjectURL(localImage.url);
+    }
+  },
+
+  // Checks if remoteImage and localImage are the same.
+  isRemoteImageLocal(localImage, remoteImage) {
+    // Both remoteImage and localImage are present.
+    if (remoteImage && localImage) {
+      return this.isBlob(false, remoteImage) ?
+             localImage.path === remoteImage.path :
+             localImage.url === remoteImage;
+    }
+
+    // This will only handle the remaining three possible outcomes.
+    // (i.e. everything except when both image and localImage are present)
+    return !remoteImage && !localImage;
+  }
+};