Stop calling blink::shutdown in content/ tests

As discussed in blink-dev@ (https://groups.google.com/a/chromium.org/d/topic/blink-dev/kk4VX0xRB7I/discussion)
and platform-architecture-dev@ (https://groups.google.com/a/chromium.org/d/topic/platform-architecture-dev/Zc12k91NTFk/discussion),
there is no reason we have to shut down the renderer gracefully.
It's just causing use-after-free bugs and wasting performance.
This CL stops calling blink::shutdown in content/ tests.

BUG=639244

Review-Url: https://codereview.chromium.org/2268283004
Cr-Commit-Position: refs/heads/master@{#414234}

content/public/test/render_view_test.cc

@@ -339,17 +339,12 @@ void RenderViewTest::TearDown() {
   base::RunLoop().RunUntilIdle();
 
 #if defined(OS_MACOSX)
-  // Needs to run before blink::shutdown().
   autorelease_pool_.reset(NULL);
 #endif
 
   leak_detector->collectGarbageAndReport();
 
-  base::RunLoop().RunUntilIdle();
-
   blink_platform_impl_.Shutdown();
-  blink::shutdown();
-
   platform_->PlatformUninitialize();
   platform_.reset();
   params_.reset();

content/test/test_blink_web_unit_test_support.cc

@@ -153,7 +153,6 @@ TestBlinkWebUnitTestSupport::~TestBlinkWebUnitTestSupport() {
   mock_clipboard_.reset();
   if (renderer_scheduler_)
     renderer_scheduler_->Shutdown();
-  blink::shutdown();
 
   // Clear the FeatureList that was registered in the constructor.
   base::FeatureList::ClearInstanceForTesting();