Remove trailing backslash in comment causing multiline comment warning.

chrome/browser/extensions/api/certificate_provider/certificate_provider_apitest.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include <openssl/evp.h>
 #include <openssl/rsa.h>
 #include <stddef.h>
 #include <stdint.h>
 #include <stdlib.h>
 
@@ skipping 225 matching lines @@
   {
     base::RunLoop run_loop;
     std::string https_reply;
     https_contents->GetMainFrame()->ExecuteJavaScriptForTests(
         base::ASCIIToUTF16("document.body.textContent;"),
         base::Bind(&StoreString, &https_reply, run_loop.QuitClosure()));
     run_loop.Run();
     // Expect the server to return the fingerprint of the client cert that we
     // presented, which should be the fingerprint of 'l1_leaf.der'.
     // The fingerprint can be calculated independently using:
-    // openssl x509 -inform DER -noout -fingerprint -in \
+    // openssl x509 -inform DER -noout -fingerprint -in
     //   chrome/test/data/extensions/api_test/certificate_provider/l1_leaf.der
     ASSERT_EQ(
         "got client cert with fingerprint: "
         "2ab3f55e06eb8b36a741fe285a769da45edb2695",
         https_reply);
   }
 
   // Replying to the same signature request a second time must fail.
   {
     base::RunLoop run_loop;
     const std::string code = "replyWithSignatureSecondTime();";
     bool result = false;
     extension_contents->GetMainFrame()->ExecuteJavaScriptForTests(
         base::ASCIIToUTF16(code),
         base::Bind(&StoreBool, &result, run_loop.QuitClosure()));
     run_loop.Run();
     EXPECT_TRUE(result);
   }
 }