Fix FetchUrlTest memory leak.

FetchUrlTest calls mojo::core::Init() for each test.
This is uneccessary and causing failure on exit in asan builder.

Bug: 1018424
Change-Id: I61d66a532dfcc08987ba18df7e1cee18be657a90
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1966694Reviewed-by: John Chen <johnchen@chromium.org>
Commit-Queue: Ilia Samsonov <isamsonov@google.com>
Cr-Commit-Position: refs/heads/master@{#724558}

chrome/test/chromedriver/net/net_util_unittest.cc

@@ -49,8 +49,6 @@ class FetchUrlTest : public testing::Test,
         FROM_HERE, base::BindOnce(&FetchUrlTest::InitOnIO,
                                   base::Unretained(this), &event));
 
-    mojo::core::Init();
-
     event.Wait();
   }
 
@@ -63,6 +61,8 @@ class FetchUrlTest : public testing::Test,
     event.Wait();
   }
 
+  static void SetUpTestSuite() { mojo::core::Init(); }
+
   void InitOnIO(base::WaitableEvent* event) {
     scoped_refptr<URLRequestContextGetter> context_getter =
         new URLRequestContextGetter(io_thread_.task_runner());