Improve usage of window rectangles

* Skips non-AA diff rect elements and replaces them with window
  rectangles.
* Places window rectangles in the interiors of antialiased diff rects.
* Arranges two overlapping window rectangles in a plus shape inside of
  diff rounded rects.
* Enables window rectangles when clearing and generating clip masks.

GTX 960 perf result (with vs. without window rectangles):

                              glinst4                msaa16                 gpu
keymobi_pinterest.skp         0.48 -> 0.17 [ 35%]    2.77 -> 1.49 [ 54%]    0.22 -> 0.16 [ 70%]
keymobi_digg_com.skp          0.42 -> 0.23 [ 55%]    2.34 -> 1.08 [ 46%]    0.25 -> 0.21 [ 83%]
desk_jsfiddlebigcar.skp       0.28 -> 0.16 [ 59%]    1.70 -> 0.96 [ 57%]    0.19 -> 0.14 [ 70%]
top25desk_wordpress.skp       0.45 -> 0.18 [ 40%]    2.78 -> 1.53 [ 55%]    0.21 -> 0.19 [ 94%]
top25desk_weather_com.skp     2.01 -> 1.93 [ 96%]    23.5 -> 2.54 [ 11%]    1.90 -> 1.68 [ 88%]
keymobi_blogger.skp           0.57 -> 0.37 [ 65%]    2.87 -> 1.54 [ 54%]    0.43 -> 0.33 [ 77%]
keymobi_linkedin.skp          0.32 -> 0.17 [ 51%]    1.93 -> 1.04 [ 54%]    0.17 -> 0.15 [ 91%]
keymobi_bing_com_search_...   0.29 -> 0.25 [ 83%]    1.85 -> 1.23 [ 66%]    0.50 -> 0.24 [ 48%]
keymobi_theverge_com_201...   1.00 -> 0.67 [ 68%]    9.46 -> 3.84 [ 41%]    0.72 -> 0.65 [ 90%]
keymobi_sfgate_com_.skp       1.56 -> 1.13 [ 72%]    4.49 -> 2.86 [ 64%]    1.54 -> 1.11 [ 72%]
...
GEOMEAN (All 79 blink skps)   1.04 -> 0.90 [ 86%]    4.22 -> 2.81 [ 67%]    0.95 -> 0.89 [ 94%]

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2289363005

Committed: https://skia.googlesource.com/skia/+/db42be9a326c747ff92ed1da8c3536c5b3e8e22b
Review-Url: https://codereview.chromium.org/2289363005
diff --git a/include/gpu/GrTypesPriv.h b/include/gpu/GrTypesPriv.h
index 8c42d64..d60fab1 100644
--- a/include/gpu/GrTypesPriv.h
+++ b/include/gpu/GrTypesPriv.h
@@ -9,7 +9,6 @@
 #define GrTypesPriv_DEFINED
 
 #include "GrTypes.h"
-#include "SkRect.h"
 #include "SkRefCnt.h"
 
  /**
@@ -420,32 +419,6 @@
     kRW_GrIOType
 };
 
-struct GrScissorState {
-    GrScissorState() : fEnabled(false) {}
-    GrScissorState(const SkIRect& rect) : fEnabled(true), fRect(rect) {}
-    void setDisabled() { fEnabled = false; }
-    void set(const SkIRect& rect) { fRect = rect; fEnabled = true; }
-    bool SK_WARN_UNUSED_RESULT intersect(const SkIRect& rect) {
-        if (!fEnabled) {
-            this->set(rect);
-            return true;
-        }
-        return fRect.intersect(rect);
-    }
-    bool operator==(const GrScissorState& other) const {
-        return fEnabled == other.fEnabled &&
-                (false == fEnabled || fRect == other.fRect);
-    }
-    bool operator!=(const GrScissorState& other) const { return !(*this == other); }
-
-    bool enabled() const { return fEnabled; }
-    const SkIRect& rect() const { return fRect; }
-
-private:
-    bool    fEnabled;
-    SkIRect fRect;
-};
-
 /**
 * Indicates the type of data that a GPU buffer will be used for.
 */
diff --git a/include/private/GrSurfaceProxy.h b/include/private/GrSurfaceProxy.h
index 98979ac..69656fe 100644
--- a/include/private/GrSurfaceProxy.h
+++ b/include/private/GrSurfaceProxy.h
@@ -9,6 +9,7 @@
 #define GrSurfaceProxy_DEFINED
 
 #include "GrGpuResource.h"
+#include "SkRect.h"
 
 class GrTextureProxy;
 class GrRenderTargetProxy;