DM: Add support for reading a directory of images with --expectations (-r).

dm/DMWriteTask.h

 #ifndef DMWriteTask_DEFINED
 #define DMWriteTask_DEFINED
 
+#include "DMExpectations.h"
 #include "DMTask.h"
 #include "SkBitmap.h"
 #include "SkString.h"
 #include "SkTArray.h"
 
+
 // Writes a bitmap to a file.
 
 namespace DM {
 
 class WriteTask : public Task {
 
 public:
     WriteTask(const Task& parent,  // WriteTask must be a child Task.  Pass its parent here.
               SkBitmap bitmap);    // Bitmap to write.
 
     virtual void draw() SK_OVERRIDE;
     virtual bool usesGpu() const SK_OVERRIDE { return false; }
     virtual bool shouldSkip() const SK_OVERRIDE;
     virtual SkString name() const SK_OVERRIDE;
 
+    // Reads image files WriteTask wrote under root and compares them with bitmap.
+    class Expectations : public DM::Expectations {
+    public:
+        explicit Expectations(const char* root) : fRoot(root) {}
+
+        bool check(const Task& task, SkBitmap bitmap) const SK_OVERRIDE;
+    private:
+        const char* fRoot;
+    };
+
 private:
     SkTArray<SkString> fSuffixes;
     SkString fGmName;
     const SkBitmap fBitmap;
 
     void makeDirOrFail(SkString dir);
 };
 
 }  // namespace DM
 
 #endif  // DMWriteTask_DEFINED