DevTools: Support XHR event listener breakpoints on frontend.

LayoutTests/inspector/sources/debugger/event-listener-breakpoints-xhr-expected.txt

Index: LayoutTests/inspector/sources/debugger/event-listener-breakpoints-xhr-expected.txt
diff --git a/LayoutTests/inspector/sources/debugger/event-listener-breakpoints-xhr-expected.txt b/LayoutTests/inspector/sources/debugger/event-listener-breakpoints-xhr-expected.txt
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+Tests event listener breakpoints on XHRs.
+
+Set timer for test function.
+Captured call stacks in no particular order:
+Call stack:
+    0) downloadEnd (event-listener-breakpoints-xhr.html:19)
+Event name: listener:loadend
+Event target: XMLHttpRequest
+
+Call stack:
+    0) downloadProgress (event-listener-breakpoints-xhr.html:27)
+Event name: listener:progress
+Event target: XMLHttpRequest
+
+Call stack:
+    0) loadCallback (event-listener-breakpoints-xhr.html:35)
+Event name: listener:load
+Event target: XMLHttpRequest
+
+Call stack:
+    0) uploadEnd (event-listener-breakpoints-xhr.html:23)
+Event name: listener:loadend
+Event target: XMLHttpRequestUpload
+
+Call stack:
+    0) uploadProgress (event-listener-breakpoints-xhr.html:31)
+Event name: listener:progress
+Event target: XMLHttpRequestUpload
+
+Call stack:
+    0) xhr.onreadystatechange (event-listener-breakpoints-xhr.html:15)
+    1) sendXHR (event-listener-breakpoints-xhr.html:46)
+    2) testFunction (event-listener-breakpoints-xhr.html:9)
+Event name: listener:readystatechange
+Event target: XMLHttpRequest
+
+