Auto merge of #24870 - pshaughn:2909, r=jdm

Fix #2909 (squashed version of PR #24865)

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Now using data-url::forgiving_base64 instead of base64, this fixes all the fetch/data-urls/base64.* tests.

---
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- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes do not quite fix yet #2909

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- [X] There are tests for these changes OR
- [ ] These changes do not require tests because ___

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Cargo.lock

@@ -1021,6 +1021,15 @@ dependencies = [
  "syn 1.0.3",
 ]
 
+[[package]]
+name = "data-url"
+version = "0.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d33fe99ccedd6e84bc035f1931bb2e6be79739d6242bd895e7311c886c50dc9c"
+dependencies = [
+ "matches",
+]
+
 [[package]]
 name = "dbus"
 version = "0.6.3"
@@ -3460,6 +3469,7 @@ dependencies = [
  "content-security-policy",
  "cookie",
  "crossbeam-channel",
+ "data-url",
  "devtools_traits",
  "embedder_traits",
  "flate2",