Fix SkNWayCanvas to prevent crashes by setting up a device

This is a cherry-pick of two CL's from upstream Skia:
https://codereview.appspot.com/6092056/
https://codereview.appspot.com/6131062/

bug: 6400332
Change-Id: Ia833e7c0d4fd6e21a06980653450095176f5bd42

4 files changed, 20 insertions, 3 deletions

diff --git a/include/utils/SkNWayCanvas.h b/include/utils/SkNWayCanvas.h
index 69c1fcf..dbf4a58 100644
--- a/include/utils/SkNWayCanvas.h
+++ b/include/utils/SkNWayCanvas.h
@@ -13,7 +13,7 @@
 
 class SkNWayCanvas : public SkCanvas {
 public:
-    SkNWayCanvas();
+    SkNWayCanvas(int width, int height);
     virtual ~SkNWayCanvas();
 
     void addCanvas(SkCanvas*);
diff --git a/src/core/SkCanvas.cpp b/src/core/SkCanvas.cpp
index aa92dd0..7861636 100644
--- a/src/core/SkCanvas.cpp
+++ b/src/core/SkCanvas.cpp
@@ -573,6 +573,9 @@ bool SkCanvas::readPixels(SkBitmap* bitmap,
 
 bool SkCanvas::readPixels(const SkIRect& srcRect, SkBitmap* bitmap) {
     SkDevice* device = this->getDevice();
+    if (!device) {
+        return false;
+    }
 
     SkIRect bounds;
     bounds.set(0, 0, device->width(), device->height());
@@ -1058,6 +1061,10 @@ static bool clipPathHelper(const SkCanvas* canvas, SkRasterClip* currClip,
         }
     } else {
         const SkDevice* device = canvas->getDevice();
+        if (!device) {
+            return currClip->setEmpty();
+        }
+
         base.setRect(0, 0, device->width(), device->height());
 
         if (SkRegion::kReplace_Op == op) {
@@ -1114,6 +1121,11 @@ bool SkCanvas::clipRegion(const SkRegion& rgn, SkRegion::Op op) {
 void SkCanvas::validateClip() const {
     // construct clipRgn from the clipstack
     const SkDevice* device = this->getDevice();
+    if (!device) {
+        SkASSERT(this->getTotalClip().isEmpty());
+        return;
+    }
+
     SkIRect ir;
     ir.set(0, 0, device->width(), device->height());
     SkRasterClip tmpClip(ir);
diff --git a/src/utils/SkNWayCanvas.cpp b/src/utils/SkNWayCanvas.cpp
index 06cf32d..9f6ebc6 100644
--- a/src/utils/SkNWayCanvas.cpp
+++ b/src/utils/SkNWayCanvas.cpp
@@ -7,7 +7,11 @@
  */
 #include "SkNWayCanvas.h"
 
-SkNWayCanvas::SkNWayCanvas() {}
+SkNWayCanvas::SkNWayCanvas(int width, int height) {
+    SkBitmap bm;
+    bm.setConfig(SkBitmap::kNo_Config, width, height);
+    this->setBitmapDevice(bm);
+}
 
 SkNWayCanvas::~SkNWayCanvas() {
     this->removeAll();
diff --git a/tests/CanvasTest.cpp b/tests/CanvasTest.cpp
index 7cafda2..76573ed 100644
--- a/tests/CanvasTest.cpp
+++ b/tests/CanvasTest.cpp
@@ -691,7 +691,8 @@ static void TestNWayCanvasStateConsistency(
     SkDevice indirectDevice2(indirectStore2);
     SkCanvas indirectCanvas2(&indirectDevice2);
 
-    SkNWayCanvas nWayCanvas;
+    SkISize canvasSize = referenceCanvas.getDeviceSize();
+    SkNWayCanvas nWayCanvas(canvasSize.width(), canvasSize.height());
     nWayCanvas.addCanvas(&indirectCanvas1);
     nWayCanvas.addCanvas(&indirectCanvas2);