arc: Fix Default icon issue when cached icon file is corrupted.

components/arc/test/fake_app_instance.h

Index: components/arc/test/fake_app_instance.h
diff --git a/components/arc/test/fake_app_instance.h b/components/arc/test/fake_app_instance.h
index 4557cad5739472ace60ddaf2bfd3100ae6dabe07..1d84e5cc634ca37fd428caac0775ea0c702e6080 100644
--- a/components/arc/test/fake_app_instance.h
+++ b/components/arc/test/fake_app_instance.h
@@ -125,6 +125,9 @@ class FakeAppInstance : public mojom::AppInstance {
   bool GenerateAndSendIcon(const mojom::AppInfo& app,
                            mojom::ScaleFactor scale_factor,
                            std::string* png_data_as_string);
+  void GenerateAndSendBadIcon(const mojom::AppInfo& app,
+                              mojom::ScaleFactor scale_factor,
+                              std::string* png_data_as_string);

[Luis Héctor Chávez, 2017/03/15 20:28:52]

can you convert this to a std::vector<uint8_t>*? std::string seems like a bad
abstraction for binary data.

[lgcheng, 2017/03/15 22:05:34]

In fact the std::string* png_data_as_string is not need in the test I added. I
remove the last argument.
But for the existing functions,  base::ReadFileToString is used to read binary,
so I'd not touch std::string* png_data_as_string there. WDYT?

[Luis Héctor Chávez, 2017/03/15 22:49:50]

I see, the removal of this parameter sgtm.

The other usage is kind of unfortunate though :/ I think I'm begrudgingly fine
with leaving that one as-is since this is testing-only code.

   void SendInstallShortcut(const mojom::ShortcutInfo& shortcuts);
   void SendInstallShortcuts(const std::vector<mojom::ShortcutInfo>& shortcuts);
   void SetTaskInfo(int32_t task_id,