Merge pull request #5413 from electron/process-resource-usage

Fetch Process resource usage from WebContents

docs/api/web-frame.md

@@ -106,4 +106,43 @@ In the browser window some HTML APIs like `requestFullScreen` can only be
 invoked by a gesture from the user. Setting `userGesture` to `true` will remove
 this limitation.
 
+### `webFrame.getResourceUsage()`
+
+Returns an object describing usage information of Blink's internal memory
+caches.
+
+```javascript
+console.log(webFrame.getResourceUsage())
+```
+
+This will generate:
+
+```javascript
+{
+  images: {
+    count: 22,
+    size: 2549,
+    liveSize: 2542,
+    decodedSize: 478,
+    purgedSize: 0,
+    purgeableSize: 0
+  },
+  cssStyleSheets: { /* same with "images" */ },
+  xslStyleSheets: { /* same with "images" */ },
+  fonts: { /* same with "images" */ },
+  other: { /* same with "images" */ },
+}
+```
+
+### `webFrame.clearCache()`
+
+Attempts to free memory that is no longer being used (like images from a
+previous navigation).
+
+Note that blindly calling this method probably makes Electron slower since it
+will have to refill these emptied caches, you should only call it if an event
+in your app has occured that makes you think your page is actually using less
+memory (i.e. you have navigated from a super heavy page to a mostly empty one,
+and intend to stay there).
+
 [spellchecker]: https://github.com/atom/node-spellchecker