[Media Router tests] Add minimal ScopedAllowIO for the tests to pass.

chrome/test/media_router/media_router_integration_browsertest.cc

Index: chrome/test/media_router/media_router_integration_browsertest.cc
diff --git a/chrome/test/media_router/media_router_integration_browsertest.cc b/chrome/test/media_router/media_router_integration_browsertest.cc
index ff88be48d2fdbf023220b2cd6ee90f269ef2360b..78b2abf74ad4469ddc8438bd301d1ab86efd54e2 100644
--- a/chrome/test/media_router/media_router_integration_browsertest.cc
+++ b/chrome/test/media_router/media_router_integration_browsertest.cc
@@ -13,6 +13,7 @@
 #include "base/json/json_writer.h"
 #include "base/path_service.h"
 #include "base/strings/stringprintf.h"
+#include "base/threading/thread_restrictions.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/ui/browser_finder.h"
@@ -279,6 +280,8 @@ void MediaRouterIntegrationBrowserTest::CheckDialogRemainsOpen(
 
 void MediaRouterIntegrationBrowserTest::SetTestData(
     base::FilePath::StringPieceType test_data_file) {
+  // crbug.com/724573
+  base::ThreadRestrictions::ScopedAllowIO allow_io;

[mark a. foltz, 2017/05/30 23:50:04]

I don't see anything in this stack frame that requires IO.
Did I miss something?

[imcheng, 2017/05/31 00:30:22]

JSONFileValueDeserializer::Deserialize requires it. I scoped allow_io to only
that call.

   base::FilePath full_path = GetResourceFile(test_data_file);
   JSONFileValueDeserializer deserializer(full_path);
   int error_code = 0;
@@ -312,6 +315,8 @@ WebContents* MediaRouterIntegrationBrowserTest::OpenMRDialog(
 
 base::FilePath MediaRouterIntegrationBrowserTest::GetResourceFile(
     base::FilePath::StringPieceType relative_path) const {
+  // crbug.com/724573
+  base::ThreadRestrictions::ScopedAllowIO allow_io;

[mark a. foltz, 2017/05/30 23:50:03]

Can this be scoped to only include PathExists?

[imcheng, 2017/05/31 00:30:22]

Done.

   base::FilePath base_dir;
   // ASSERT_TRUE can only be used in void returning functions.
   // Use CHECK instead in non-void returning functions.