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

dm/DMExpectations.h

+#ifndef DMExpectations_DEFINED
+#define DMExpectations_DEFINED
+
+#include "DMTask.h"
+#include "gm_expectations.h"
+
+namespace DM {
+
+struct Expectations {
+    virtual ~Expectations() {}
+
+    // Return true if bitmap is the correct output for task, else false.
+    virtual bool check(const Task& task, SkBitmap bitmap) const = 0;
+};
+
+class NoExpectations : public Expectations {
+public:
+    NoExpectations() {}
+    bool check(const Task&, SkBitmap) const SK_OVERRIDE { return true; }
+};
+
+class JsonExpectations : public Expectations {
+public:
+    explicit JsonExpectations(const char* path) : fGMExpectations(path) {}
+
+    bool check(const Task& task, SkBitmap bitmap) const SK_OVERRIDE {
+        SkString filename = task.name();
+        filename.append(".png");
+        const skiagm::Expectations expectations = fGMExpectations.get(filename.c_str());
+
+        if (expectations.ignoreFailure() || expectations.empty()) {
+            return true;
+        }
+
+        // Delay this calculation as long as possible.  It's expensive.
+        const skiagm::GmResultDigest digest(bitmap);
+        return expectations.match(digest);
+    }
+
+private:
+    skiagm::JsonExpectationsSource fGMExpectations;
+};
+
+}  // namespace DM
+
+#endif // DMExpectations_DEFINED