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

dm/DMExpectationsTask.cpp

Index: dm/DMExpectationsTask.cpp
diff --git a/dm/DMExpectationsTask.cpp b/dm/DMExpectationsTask.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..cb92486269890d8c2567ac4a660b8deb59468605
--- /dev/null
+++ b/dm/DMExpectationsTask.cpp
@@ -0,0 +1,21 @@
+#include "DMExpectationsTask.h"
+#include "DMUtil.h"
+
+namespace DM {
+
+ExpectationsTask::ExpectationsTask(const Task& parent,
+                                   const Expectations& expectations,
+                                   SkBitmap bitmap)
+    : Task(parent)
+    , fName(parent.name())  // Masquerade as parent so failures are attributed to it.
+    , fExpectations(expectations)
+    , fBitmap(bitmap)
+    {}
+
+void ExpectationsTask::draw() {
+    if (!fExpectations.check(*this, fBitmap)) {
+        this->fail();
+    }
+}
+
+}  // namespace DM