add isRect() check to AAClip, to detect if a soft-clip is really just an irect

tests/AAClipTest.cpp

Index: tests/AAClipTest.cpp
diff --git a/tests/AAClipTest.cpp b/tests/AAClipTest.cpp
index 26c1ec1d0e21c30e2ce40095ed46a24dd497f92d..776cd5267ab6a4a31022394072f78fe4cd462b2d 100644
--- a/tests/AAClipTest.cpp
+++ b/tests/AAClipTest.cpp
@@ -318,6 +318,30 @@ static void test_path_with_hole(skiatest::Reporter* reporter) {
     }
 }
 
+static void test_really_a_rect(skiatest::Reporter* reporter) {
+    SkRRect rrect;
+    rrect.setRectXY(SkRect::MakeWH(100, 100), 5, 5);
+
+    SkPath path;
+    path.addRRect(rrect);
+
+    SkAAClip clip;
+    clip.setPath(path);
+
+    REPORTER_ASSERT(reporter, clip.getBounds() == SkIRect::MakeWH(100, 100));
+    REPORTER_ASSERT(reporter, !clip.isRect());
+
+    // This rect should intersect the clip, but slice-out all of the "soft" parts,
+    // leaving just a rect.
+    const SkIRect ir = SkIRect::MakeLTRB(10, -10, 50, 90);
+    
+    clip.op(ir, SkRegion::kIntersect_Op);
+
+    REPORTER_ASSERT(reporter, clip.getBounds() == SkIRect::MakeLTRB(10, 0, 50, 90));
+    // the clip recognized that that it is just a rect!
+    REPORTER_ASSERT(reporter, clip.isRect());
+}
+
 #include "SkRasterClip.h"
 
 static void copyToMask(const SkRasterClip& rc, SkMask* mask) {
@@ -404,4 +428,5 @@ DEF_TEST(AAClip, reporter) {
     test_path_with_hole(reporter);
     test_regressions();
     test_nearly_integral(reporter);
+    test_really_a_rect(reporter);
 }