Initial error handling code

include/core/SkRect.h

Index: include/core/SkRect.h
diff --git a/include/core/SkRect.h b/include/core/SkRect.h
index c615603d7e85b1d7adb645c20390a402f0c8f908..d8343b4005bbbff759572f81a8bca408b9833bc7 100644
--- a/include/core/SkRect.h
+++ b/include/core/SkRect.h
@@ -100,6 +100,8 @@ struct SK_API SkIRect {
      */
     bool isEmpty() const { return fLeft >= fRight || fTop >= fBottom; }
 
+    bool isInverted() const { return fLeft > fRight || fTop > fBottom; }
+
     bool isLargest() const { return SK_MinS32 == fLeft &&
                                     SK_MinS32 == fTop &&
                                     SK_MaxS32 == fRight &&
@@ -425,11 +427,19 @@ struct SK_API SkRect {
      */
     bool isEmpty() const { return fLeft >= fRight || fTop >= fBottom; }
 
+    bool isInverted() const { return fLeft > fRight || fTop > fBottom; }
+
     bool isLargest() const { return SK_ScalarMin == fLeft &&
                                     SK_ScalarMin == fTop &&
                                     SK_ScalarMax == fRight &&
                                     SK_ScalarMax == fBottom; }
 
+    bool isValid() const { return SkScalarIsFinite(fLeft) &&
+                                  SkScalarIsFinite(fTop) &&
+                                  SkScalarIsFinite(fRight) &&
+                                  SkScalarIsFinite(fBottom) &&
+                                  (fLeft <= fRight) &&
+                                  (fTop <= fBottom); }
     /**
      *  Returns true iff all values in the rect are finite. If any are
      *  infinite or NaN (or SK_FixedNaN when SkScalar is fixed) then this