Avoid re-rendering stencil clip for every draw with reducable clip stack

tests/ClipCacheTest.cpp

Index: tests/ClipCacheTest.cpp
diff --git a/tests/ClipCacheTest.cpp b/tests/ClipCacheTest.cpp
index fab1f58dd70609887a12fa47fcc98db62e95ff00..070f8eb46900ec0c780ee33a5a8db869de455896 100644
--- a/tests/ClipCacheTest.cpp
+++ b/tests/ClipCacheTest.cpp
@@ -106,7 +106,6 @@ static void check_state(skiatest::Reporter* reporter,
                         const SkClipStack& clip,
                         GrTexture* mask,
                         const SkIRect& bound) {
-    SkClipStack cacheClip;
     REPORTER_ASSERT(reporter, clip.getTopmostGenID() == cache.getLastClipGenID());
 
     REPORTER_ASSERT(reporter, mask == cache.getLastMask());
@@ -116,6 +115,19 @@ static void check_state(skiatest::Reporter* reporter,
     REPORTER_ASSERT(reporter, bound == cacheBound);
 }
 
+static void check_empty_state(skiatest::Reporter* reporter,
+                              const GrClipMaskCache& cache) {
+    REPORTER_ASSERT(reporter, SkClipStack::kInvalidGenID == cache.getLastClipGenID());
+    REPORTER_ASSERT(reporter, NULL == cache.getLastMask());
+
+    SkIRect emptyBound;
+    emptyBound.setEmpty();
+
+    SkIRect cacheBound;
+    cache.getLastBound(&cacheBound);
+    REPORTER_ASSERT(reporter, emptyBound == cacheBound);
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 // basic test of the cache's base functionality:
 //  push, pop, set, canReuse & getters
@@ -128,14 +140,8 @@ static void test_cache(skiatest::Reporter* reporter, GrContext* context) {
 
     cache.setContext(context);
 
-    SkClipStack emptyClip;
-    emptyClip.reset();
-
-    SkIRect emptyBound;
-    emptyBound.setEmpty();
-
     // check initial state
-    check_state(reporter, cache, emptyClip, NULL, emptyBound);
+    check_empty_state(reporter, cache);
 
     // set the current state
     SkIRect bound1;
@@ -165,7 +171,7 @@ static void test_cache(skiatest::Reporter* reporter, GrContext* context) {
     cache.push();
 
     // verify that the pushed state is initially empty
-    check_state(reporter, cache, emptyClip, NULL, emptyBound);
+    check_empty_state(reporter, cache);
     REPORTER_ASSERT(reporter, texture1->getRefCnt());
 
     // modify the new state
@@ -202,7 +208,7 @@ static void test_cache(skiatest::Reporter* reporter, GrContext* context) {
     cache.reset();
 
     // verify it is now empty
-    check_state(reporter, cache, emptyClip, NULL, emptyBound);
+    check_empty_state(reporter, cache);
 
     // pop again - so there is no state
     cache.pop();
@@ -210,7 +216,7 @@ static void test_cache(skiatest::Reporter* reporter, GrContext* context) {
 #if !defined(SK_DEBUG)
     // verify that the getters don't crash
     // only do in release since it generates asserts in debug
-    check_state(reporter, cache, emptyClip, NULL, emptyBound);
+    check_empty_state(reporter, cache);
 #endif
 }