Add TestBrowserThreadBundle into RenderViewHostTestHarness. Kill some unnecessary real threads.

content/browser/devtools/devtools_manager_unittest.cc

Index: content/browser/devtools/devtools_manager_unittest.cc
diff --git a/content/browser/devtools/devtools_manager_unittest.cc b/content/browser/devtools/devtools_manager_unittest.cc
index 944850d2bb3f9d2ab31d361ffad544fcded78a85..0167a152a00fac629f28aa009a0aee9daf42ff7c 100644
--- a/content/browser/devtools/devtools_manager_unittest.cc
+++ b/content/browser/devtools/devtools_manager_unittest.cc
@@ -106,10 +106,6 @@ class DevToolsManagerTestBrowserClient : public TestContentBrowserClient {
 }  // namespace
 
 class DevToolsManagerTest : public RenderViewHostImplTestHarness {
- public:
-  DevToolsManagerTest() {
-  }
-
  protected:
   virtual void SetUp() OVERRIDE {
     original_browser_client_ = SetBrowserClientForTesting(&browser_client_);