ResourceFetcherTest: introduce FetchTestingPlatformSupport

third_party/WebKit/Source/platform/testing/TestingPlatformSupport.h

Index: third_party/WebKit/Source/platform/testing/TestingPlatformSupport.h
diff --git a/third_party/WebKit/Source/platform/testing/TestingPlatformSupport.h b/third_party/WebKit/Source/platform/testing/TestingPlatformSupport.h
index 2122f02bbaa7a0faa4d29235853934a9ab73cf8a..71aeb9c85420b75b770c39ba2cdb6384072683c1 100644
--- a/third_party/WebKit/Source/platform/testing/TestingPlatformSupport.h
+++ b/third_party/WebKit/Source/platform/testing/TestingPlatformSupport.h
@@ -114,6 +114,8 @@ class TestingPlatformSupport : public Platform {
   WebURLError cancelledError(const WebURL&) const override;
   InterfaceProvider* interfaceProvider() override;
 
+  virtual void runUntilIdle();
+
  protected:
   class TestingInterfaceProvider;
 
@@ -145,7 +147,7 @@ class TestingPlatformSupportWithMockScheduler : public TestingPlatformSupport {
   // This function ignores future delayed tasks when deciding if the system is
   // idle.  If you need to ensure delayed tasks run, try runForPeriodSeconds()
   // instead.
-  void runUntilIdle();
+  void runUntilIdle() override;
 
   // Runs for |seconds| the testing clock is advanced by |seconds|.  Note real
   // time elapsed will typically much less than |seconds| because delays between