screen_ui: Drop the dependency on common.h.

Remove the use of fopen_path() in screen_ui.cpp, as this is the only
place that requires the dependency on common.h. The mounting work should
be done by the caller.

Also change the parameter in RecoveryUI::ShowFile() from const char* to
const std::string&.

Test: mmma -j bootable/recovery
Test: Build and boot into recovery image on angler. Choose 'View
      recovery logs'.
Change-Id: I8e63f14a8e2b12b856e5a92476e4226cd6ea39fb
diff --git a/ui.h b/ui.h
index 636c2ff..c468992 100644
--- a/ui.h
+++ b/ui.h
@@ -88,7 +88,9 @@
   virtual void Print(const char* fmt, ...) __printflike(2, 3) = 0;
   virtual void PrintOnScreenOnly(const char* fmt, ...) __printflike(2, 3) = 0;
 
-  virtual void ShowFile(const char* filename) = 0;
+  // Shows the contents of the given file. Caller ensures the patition that contains the file has
+  // been mounted.
+  virtual void ShowFile(const std::string& filename) = 0;
 
   // --- key handling ---