DM: support non-fatal errors

dm/DMSrcSink.h

 #ifndef DMSrcSink_DEFINED
 #define DMSrcSink_DEFINED
 
 #include "DMGpuSupport.h"
 #include "SkBBHFactory.h"
 #include "SkBBoxHierarchy.h"
 #include "SkBitmap.h"
 #include "SkCanvas.h"
 #include "SkData.h"
 #include "SkGPipe.h"
 #include "SkPicture.h"
 #include "gm.h"
 
 namespace DM {
 
 // This is just convenience.  It lets you use either return "foo" or return SkStringPrintf(...).
 struct ImplicitString : public SkString {
     template <typename T>
     ImplicitString(const T& s) : SkString(s) {}
 };
-typedef ImplicitString Error;
 typedef ImplicitString Name;
 typedef ImplicitString Path;
 
+class Error {
+public:
+    Error(const SkString& s) : fMsg(s), fFatal(!this->isEmpty()) {}
+    Error(const char* s)     : fMsg(s), fFatal(!this->isEmpty()) {}
+
+    Error(const Error&)            = default;
+    Error& operator=(const Error&) = default;
+
+    static Error Nonfatal(const SkString& s) { return Nonfatal(s.c_str()); }
+    static Error Nonfatal(const char* s) {
+        Error e(s);
+        e.fFatal = false;
+        return e;
+    }
+
+    const char* c_str() const { return fMsg.c_str(); }
+    bool isEmpty() const { return fMsg.isEmpty(); }
+    bool isFatal() const { return fFatal; }
+
+private:
+    SkString fMsg;
+    bool     fFatal;
+};
+
 struct Src {
     // All Srcs must be thread safe.
     virtual ~Src() {}
     virtual Error SK_WARN_UNUSED_RESULT draw(SkCanvas*) const = 0;
     virtual SkISize size() const = 0;
     virtual Name name() const = 0;
 };
 
 struct Sink {
     virtual ~Sink() {}
@@ skipping 180 matching lines @@
     const char* fileExtension() const SK_OVERRIDE { return fSink->fileExtension(); }
 private:
     const int                   fW, fH;
     SkAutoTDelete<SkBBHFactory> fFactory;
     SkAutoTDelete<Sink>         fSink;
 };
 
 }  // namespace DM
 
 #endif//DMSrcSink_DEFINED