Skip Service workers in requests for mime handler plugins

BUG=808838
TEST=./browser_tests --gtest_filter=*/ServiceWorkerTest.MimeHandlerView*

Cq-Include-Trybots: master.tryserver.chromium.linux:linux_mojo
Change-Id: I82e75c200091babbab648a04232db47e2938d914
Reviewed-on: https://chromium-review.googlesource.com/914150
Commit-Queue: Rob Wu <rob@robwu.nl>
Reviewed-by: Istiaque Ahmed <lazyboy@chromium.org>
Reviewed-by: Matt Falkenhagen <falken@chromium.org>
Cr-Commit-Position: refs/heads/master@{#537386}
  void ExecuteJavaScriptForTests(const std::string& js) {
    base::RunLoop run_loop;
    browser()
        ->tab_strip_model()
        ->GetActiveWebContents()
        ->GetMainFrame()
        ->ExecuteJavaScriptForTests(
            base::ASCIIToUTF16(js),
            base::Bind([](const base::Closure& quit_callback,
                          const base::Value* result) { quit_callback.Run(); },
                       run_loop.QuitClosure()));
    run_loop.Run();
  }

  void ExecuteJavaScriptForTests(const std::string& js) {
    base::RunLoop run_loop;
    browser()
        ->tab_strip_model()
        ->GetActiveWebContents()
        ->GetMainFrame()
        ->ExecuteJavaScriptForTests(
            base::ASCIIToUTF16(js),
            base::Bind([](const base::Closure& quit_callback,
                          const base::Value* result) { quit_callback.Run(); },
                       run_loop.QuitClosure()));
    run_loop.Run();
  }
