Enable hot reloading for Blazor inside an iframe

[Copilot]

Fixes hot reload functionality for Blazor applications running inside iframes by allowing Sec-Fetch-Dest: frame and Sec-Fetch-Dest: iframe requests to trigger browser refresh script injection.

Problem

Hot Reload on Blazor apps doesn't work inside iframes because the BrowserRefreshMiddleware.IsBrowserDocumentRequest() method only accepts requests with Sec-Fetch-Dest: document. Requests from iframes use Sec-Fetch-Dest: frame or Sec-Fetch-Dest: iframe, causing the middleware to reject them and skip script injection.

This prevents hot reload from working in scenarios like:

• Blazing Story (Storybook clone for Blazor) which hosts component previews in iframes
• Any other tooling that embeds Blazor apps within iframe contexts

Solution

Updated the IsBrowserDocumentRequest method to also accept "frame" and "iframe" values for the Sec-Fetch-Dest header, in addition to the existing "document" value. This allows the browser refresh middleware to inject hot reload scripts into iframe-embedded Blazor applications.

The change is minimal and surgical - it only adds two additional string comparisons to the existing validation logic without affecting any other functionality.

Testing

• Updated existing tests to reflect the new behavior
• Split the test case to validate that frame/iframe requests now return true while other values like "serviceworker" still return false
• All 104 tests in the BrowserRefresh test suite pass

Addresses the "escape hatch" API request mentioned in the original issue for enabling hot reloading in iframe scenarios.

Original prompt

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This section details on the original issue you should resolve

<issue_title>[Hot Reload] Enable hot reloading for Blazor inside an iframe</issue_title>
<issue_description>## Description

Hot Reload on a Blazor app doesn't work inside an iframe. See the attached video and sample code.

2024-02-29_08h08_22.mp4

Sample code: 📦BlazorWasmApp1.zip

The solution I'd like

I know this is intentional by design, as mentioned in the pull request: #21954. However, some edge cases exist where hot reloading support inside an iframe is essential. For instance, the clone of Storybook for Blazor, "Blazing Story" (https://github.com/jsakamoto/BlazingStory), requires such ability because it has to host a preview of the story using an iframe.

Therefore, I hope we have a public "escape hatch" API allowing developers to explicitly enable hot reloading inside an iframe for such a particular scenario.</issue_description>

<agent_instructions>
Update

sdk/src/BuiltInTools/BrowserRefresh/BrowserRefreshMiddleware.cs

Line 72 in 92f29cd

!string.Equals(values[0], "document", StringComparison.OrdinalIgnoreCase))

to include the "frame" and "iframe" values for the Sec-Fetch-Dest header.</agent_instructions>

Comments on the Issue (you are @copilot in this section)

@MackinnonBuck We might be able to address this in one of two ways: 1. Update [this line](https://github.com/dotnet/sdk/blob/92f29cd70039b793cdcaf2321fa9bff95afc3ec1/src/BuiltInTools/BrowserRefresh/BrowserRefreshMiddleware.cs#L72) to include the "frame" and "iframe" values for the `Sec-Fetch-Dest` header. 2. Address this as part of https://github.com/dotnet/aspnetcore/issues/45213

Fixes #51005

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