Use FILE thread for disk operations in TraceSubscriberStdio

content/browser/trace_subscriber_stdio_unittest.cc

Index: content/browser/trace_subscriber_stdio_unittest.cc
===================================================================
--- content/browser/trace_subscriber_stdio_unittest.cc	(revision 120564)
+++ content/browser/trace_subscriber_stdio_unittest.cc	(working copy)
@@ -5,10 +5,27 @@
 #include "content/browser/trace_subscriber_stdio.h"
 
 #include "base/scoped_temp_dir.h"
+#include "base/threading/thread_restrictions.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace {
 
+class ScopedDisallowIO {
+ public:
+  ScopedDisallowIO() {
+    previous_value_ = base::ThreadRestrictions::SetIOAllowed(false);
+  }
+
+  ~ScopedDisallowIO() {
+    base::ThreadRestrictions::SetIOAllowed(previous_value_);
+  }
+
+ private:
+  bool previous_value_;
+
+  DISALLOW_COPY_AND_ASSIGN(ScopedDisallowIO);
+};
+
 class TraceSubscriberStdioTest : public testing::Test {
  public:
   virtual void SetUp() {
@@ -29,6 +46,10 @@
 }  // namespace
 
 TEST_F(TraceSubscriberStdioTest, CanWriteDataToFile) {
+  // TraceSubscriber callbacks are documented to occur on the UI thread,
+  // so this class must work with ThreadRestictions::SetIOAllowed(false);
+  ScopedDisallowIO scoped_disallow_io;
+
   TraceSubscriberStdio subscriber(trace_file_);
   subscriber.OnTraceDataCollected("[foo]");
   subscriber.OnTraceDataCollected("[bar]");
@@ -37,4 +58,3 @@
   subscriber.OnEndTracingComplete();
   EXPECT_FALSE(subscriber.IsValid());
 }
-