Add a test to ensure we report error when non base64 string is passed for binary param

Bug: 1140420
Change-Id: Ia2b704e0e2146dfb7e71406126e101c06fbffd5e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2514800Reviewed-by: Sigurd Schneider <sigurds@chromium.org>
Commit-Queue: Andrey Kosyakov <caseq@chromium.org>
Cr-Commit-Position: refs/heads/master@{#823613}

third_party/blink/web_tests/http/tests/inspector-protocol/fetch/fetch-post-data-continue-expected.txt

 Test post data interception
 binary string
+error when passing body as string: Failed to deserialize params.postData - BINDINGS: binary value expected <somewhere>
 

third_party/blink/web_tests/http/tests/inspector-protocol/fetch/fetch-post-data-continue.js

@@ -21,5 +21,21 @@
     }),
   ]);
   testRunner.log(event.params.args[0].value);
+
+  session.evaluate(`
+    fetch('${testRunner.url('./resources/post-echo.pl')}', {
+      method: 'post',
+      body: 'hello'
+    })`);
+  const requestPaused2 = await dp.Fetch.onceRequestPaused();
+  const {error} = await dp.Fetch.continueRequest({
+    requestId: requestPaused2.params.requestId,
+    postData: '¯\_(ツ)_/¯ not a base64 string ¯\_(ツ)_/¯'});
+
+  function trimErrorMessage(message) {
+    return message.replace(/at position \d+/, "<somewhere>");
+  }
+  testRunner.log(`error when passing body as string: ${trimErrorMessage(error.data)}`);
+
   testRunner.completeTest();
 })