Replace Handle Files & Background Sync demos (#3514)

* flag demos to move

* demo demo

* readme file

* draft content

* pngs, steps: bg sync demo

* png try later

* main pass: handle files

* unique headings

* the the

* ital status

* Update background-syncs.md

* apply review

* linkfix

* lead w/ Demo app

* -todo

* del todos

Author: mikehoffms

microsoft-edge/devtools/network/reference.md

@@ -858,7 +858,7 @@ The **Requests** table displays the following columns by default:
 - **Time**. The total duration, from the start of the request to the receipt of the final byte in the response.
 - **Fulfilled by**. Whether the request was fulfilled by the HTTP cache or the app's service worker.
 
-The **Waterfall** column is off by default.  To turn on the The **Waterfall** column, right-click a **Requests** table header, and then select the plain **Waterfall** menuitem that doesn't have a submenu.
+The **Waterfall** column is off by default.  To turn on the **Waterfall** column, right-click a **Requests** table header, and then select the plain **Waterfall** menuitem that doesn't have a submenu.
 
 
 <!-- ---------- -->
@@ -931,7 +931,7 @@ To group requests by iframes:
 
 Use the **Waterfall** column of the **Requests** pane to view the timing relationships of requests.  The default organization of the **Waterfall** column uses the start time of the requests.  So, requests that are farther to the left started earlier than the requests that are farther to the right.
 
-The **Waterfall** column is off by default.  To turn on the The **Waterfall** column, right-click a **Requests** table header, and then select the plain **Waterfall** menuitem that doesn't have a submenu.
+The **Waterfall** column is off by default.  To turn on the **Waterfall** column, right-click a **Requests** table header, and then select the plain **Waterfall** menuitem that doesn't have a submenu.
 
 To see the different ways that you can sort the Waterfall, see [Sort by activity phase](#sort-by-activity-phase), above.
 
@@ -1365,7 +1365,7 @@ For more information about each of the phases that may be displayed in the **Tim
 
 To display a preview of the timing breakdown of a request, in the **Waterfall** column of the **Requests** table, hover on the entry for the request.
 
-The **Waterfall** column is off by default.  To turn on the The **Waterfall** column, right-click a **Requests** table header, and then select the plain **Waterfall** menuitem that doesn't have a submenu.
+The **Waterfall** column is off by default.  To turn on the **Waterfall** column, right-click a **Requests** table header, and then select the plain **Waterfall** menuitem that doesn't have a submenu.
 
 ![Previewing the timing breakdown of a request](./reference-images/resources-waterfall-hover.png)
 
@@ -1428,7 +1428,7 @@ DevTools displays the timing of the `DOMContentLoaded` and `load` events in mult
 
 * In the **Overview** pane with vertical lines.
 
-* In the **Waterfall** column of the Request table with vertical lines.  The **Waterfall** column is off by default.  To turn on the The **Waterfall** column, right-click a **Requests** table header, and then select the plain **Waterfall** menuitem that doesn't have a submenu.
+* In the **Waterfall** column of the Request table with vertical lines.  The **Waterfall** column is off by default.  To turn on the **Waterfall** column, right-click a **Requests** table header, and then select the plain **Waterfall** menuitem that doesn't have a submenu.
 
 * In the **Summary** pane, at the bottom of the **Network** tool, with timing labels.
 

microsoft-edge/devtools/rendering-tools/js-runtime.md

@@ -129,7 +129,7 @@ Click the **Restore all functions** (![Restore all functions](./js-runtime-image
 
 The **Chart** view provides a visual representation of the Sampling Profile over time.
 
-After you record a memory allocation sampling profile, view the recording as a flame chart.  Select **Chart** in the the **Profile view mode** dropdown list (which initially says **Heavy (Bottom Up)**):
+After you record a memory allocation sampling profile, view the recording as a flame chart.  Select **Chart** in the **Profile view mode** dropdown list (which initially says **Heavy (Bottom Up)**):
 
 ![Flame chart view](./js-runtime-images/rendering-tools-gh-nodejs-benchmarks-run-memory-sampling-profiles-chart.png)
 

microsoft-edge/devtools/workspaces/workspace-tutorial.md

@@ -226,7 +226,7 @@ The DevTools **Workspace** tab is similar to using an editor to edit the HTML so
 
    The **index.html** tab opens in the **Sources** tool.
 
-1. In the the `<h1>` tag, replace "DevTools Workspaces Demo" with "I Love Cake".
+1. In the `<h1>` tag, replace "DevTools Workspaces Demo" with "I Love Cake".
 
    An asterisk appears next to `index.html`.