Update from https://crrev.com/320343

cc/output/software_renderer.cc

Index: cc/output/software_renderer.cc
diff --git a/cc/output/software_renderer.cc b/cc/output/software_renderer.cc
index a4b5428223e6451c881ad1260414083122c6a1cc..19c4fa3acd9c3c230f5ef9736d666347910719a0 100644
--- a/cc/output/software_renderer.cc
+++ b/cc/output/software_renderer.cc
@@ -25,6 +25,7 @@
 #include "third_party/skia/include/core/SkColor.h"
 #include "third_party/skia/include/core/SkImageFilter.h"
 #include "third_party/skia/include/core/SkMatrix.h"
+#include "third_party/skia/include/core/SkPoint.h"
 #include "third_party/skia/include/core/SkShader.h"
 #include "third_party/skia/include/effects/SkLayerRasterizer.h"
 #include "ui/gfx/geometry/rect_conversions.h"
@@ -235,7 +236,13 @@ bool SoftwareRenderer::IsSoftwareResource(
   return false;
 }
 
-void SoftwareRenderer::DoDrawQuad(DrawingFrame* frame, const DrawQuad* quad) {
+void SoftwareRenderer::DoDrawQuad(DrawingFrame* frame,
+                                  const DrawQuad* quad,
+                                  const gfx::QuadF* draw_region) {
+  if (draw_region) {
+    current_canvas_->save();
+  }
+
   TRACE_EVENT0("cc", "SoftwareRenderer::DoDrawQuad");
   gfx::Transform quad_rect_matrix;
   QuadRectTransform(&quad_rect_matrix, quad->quadTransform(), quad->rect);
@@ -270,9 +277,31 @@ void SoftwareRenderer::DoDrawQuad(DrawingFrame* frame, const DrawQuad* quad) {
     current_paint_.setXfermodeMode(SkXfermode::kSrc_Mode);
   }
 
+  if (draw_region) {
+    gfx::QuadF local_draw_region(*draw_region);
+    SkPath draw_region_clip_path;
+    local_draw_region -=
+        gfx::Vector2dF(quad->visible_rect.x(), quad->visible_rect.y());
+    local_draw_region.Scale(1.0f / quad->visible_rect.width(),
+                            1.0f / quad->visible_rect.height());
+    local_draw_region -= gfx::Vector2dF(0.5f, 0.5f);
+
+    SkPoint clip_points[4];
+    QuadFToSkPoints(local_draw_region, clip_points);
+    draw_region_clip_path.addPoly(clip_points, 4, true);
+
+    current_canvas_->clipPath(draw_region_clip_path, SkRegion::kIntersect_Op,
+                              false);
+  }
+
   switch (quad->material) {
     case DrawQuad::CHECKERBOARD:
-      DrawCheckerboardQuad(frame, CheckerboardDrawQuad::MaterialCast(quad));
+      // TODO(enne) For now since checkerboards shouldn't be part of a 3D
+      // context, clipping regions aren't supported so we skip drawing them
+      // if this becomes the case.
+      if (!draw_region) {
+        DrawCheckerboardQuad(frame, CheckerboardDrawQuad::MaterialCast(quad));
+      }
       break;
     case DrawQuad::DEBUG_BORDER:
       DrawDebugBorderQuad(frame, DebugBorderDrawQuad::MaterialCast(quad));
@@ -307,6 +336,9 @@ void SoftwareRenderer::DoDrawQuad(DrawingFrame* frame, const DrawQuad* quad) {
   }
 
   current_canvas_->resetMatrix();
+  if (draw_region) {
+    current_canvas_->restore();
+  }
 }
 
 void SoftwareRenderer::DrawCheckerboardQuad(const DrawingFrame* frame,