Implement crop rect for SkImageFilter

include/core/SkRect.h

Index: include/core/SkRect.h
diff --git a/include/core/SkRect.h b/include/core/SkRect.h
index b2f515129d05bf9a0cca392f880f0d6c75d22e25..9f3b59a38f7a29936de4dc0c9cc4564ae3472278 100644
--- a/include/core/SkRect.h
+++ b/include/core/SkRect.h
@@ -26,6 +26,12 @@ struct SK_API SkIRect {
         return r;
     }
 
+    static SkIRect SK_WARN_UNUSED_RESULT MakeLargest() {
+        SkIRect r;
+        r.setLargest();
+        return r;
+    }
+
     static SkIRect SK_WARN_UNUSED_RESULT MakeWH(int32_t w, int32_t h) {
         SkIRect r;
         r.set(0, 0, w, h);
@@ -94,6 +100,11 @@ struct SK_API SkIRect {
      */
     bool isEmpty() const { return fLeft >= fRight || fTop >= fBottom; }
 
+    bool isLargest() const { return SK_MinS32 == fLeft &&
+                                    SK_MinS32 == fTop &&
+                                    SK_MaxS32 == fRight &&
+                                    SK_MaxS32 == fBottom; }
+
     friend bool operator==(const SkIRect& a, const SkIRect& b) {
         return !memcmp(&a, &b, sizeof(a));
     }