Let DM run unit tests.

dm/DMTask.h

 #ifndef DMTask_DEFINED
 #define DMTask_DEFINED
 
 #include "DMReporter.h"
 #include "SkRunnable.h"
 #include "SkThreadPool.h"
 
 // DM will run() these tasks on one of two threadpools, depending on the result
 // of usesGpu().  The subclasses can call fail() to mark this task as failed,
 // or make any number of spawnChild() calls to kick off dependent tasks.
@@ skipping 16 matching lines @@
     virtual bool usesGpu() const = 0;
     virtual bool shouldSkip() const = 0;
     virtual SkString name() const = 0;
 
     // Returns the number of parents above this task.
     // Top-level tasks return 0, their children 1, and so on.
     int depth() const { return fDepth; }
 
 protected:
     void spawnChild(Task* task);
-    void fail();
+    void fail(const char* msg = NULL);
 
 private:
     // Both unowned.
     Reporter* fReporter;
     TaskRunner* fTaskRunner;
     int fDepth;
 
     typedef SkRunnable INHERITED;
 };
 
 }  // namespace DM
 
 #endif  // DMTask_DEFINED