Revert "Change SkCanvas to *not* inherit from SkRefCnt"

This reverts commit 824075071885b6b741c141cbe2134d8345d34589.

Reason for revert: Breaking WebView (chromium:663959)

Original change's description:
> Change SkCanvas to *not* inherit from SkRefCnt
> 
> Definitely tricky for classes like SkNWayCanvas, where the caller (today)
> need not pay attention to ownership of the canvases it gave the NWay
> (after this CL, the caller *must* managed ownership)
> 
> BUG=skia:
> 
> GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=4441
> 
> DOCS_PREVIEW= https://skia.org/?cl=4441
> 
> Change-Id: Ib1ac07a3cdf0686d78e7aaa4735d45cc90bea081
> Reviewed-on: https://skia-review.googlesource.com/4441
> Commit-Queue: Mike Reed <reed@google.com>
> Reviewed-by: Florin Malita <fmalita@chromium.org>
> Reviewed-by: Robert Phillips <robertphillips@google.com>
> 

TBR=djsollen@google.com,mtklein@google.com,halcanary@google.com,robertphillips@google.com,fmalita@chromium.org,fmalita@google.com,reed@google.com,reviews@skia.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true

Change-Id: I5e3b3e876b7d2c09833cf841801321033b6b968b
Reviewed-on: https://skia-review.googlesource.com/4687
Commit-Queue: Heather Miller <hcm@google.com>
Reviewed-by: Heather Miller <hcm@google.com>

1 files changed, 15 insertions, 10 deletions

diff --git a/src/utils/SkCanvasStateUtils.cpp b/src/utils/SkCanvasStateUtils.cpp
index 58f26b6c79..062dc13ed9 100644
--- a/src/utils/SkCanvasStateUtils.cpp
+++ b/src/utils/SkCanvasStateUtils.cpp
@@ -100,12 +100,14 @@ class SkCanvasState_v1 : public SkCanvasState {
 public:
     static const int32_t kVersion = 1;
 
-    SkCanvasState_v1(SkCanvas* canvas) : INHERITED(kVersion, canvas) {
+    SkCanvasState_v1(SkCanvas* canvas)
+    : INHERITED(kVersion, canvas)
+    {
         layerCount = 0;
         layers = nullptr;
         mcState.clipRectCount = 0;
         mcState.clipRects = nullptr;
-        originalCanvas = canvas;
+        originalCanvas = SkRef(canvas);
     }
 
     ~SkCanvasState_v1() {
@@ -116,6 +118,10 @@ public:
 
         sk_free(mcState.clipRects);
         sk_free(layers);
+
+        // it is now safe to free the canvas since there should be no remaining
+        // references to the content that is referenced by this canvas (e.g. pixels)
+        originalCanvas->unref();
     }
 
     SkMCState mcState;
@@ -278,8 +284,7 @@ static void setup_canvas_from_MC_state(const SkMCState& state, SkCanvas* canvas)
     canvas->clipRegion(clip, SkCanvas::kReplace_Op);
 }
 
-static std::unique_ptr<SkCanvas>
-make_canvas_from_canvas_layer(const SkCanvasLayerState& layerState) {
+static SkCanvas* create_canvas_from_canvas_layer(const SkCanvasLayerState& layerState) {
     SkASSERT(kRaster_CanvasBackend == layerState.type);
 
     SkBitmap bitmap;
@@ -299,15 +304,15 @@ make_canvas_from_canvas_layer(const SkCanvasLayerState& layerState) {
     SkASSERT(!bitmap.empty());
     SkASSERT(!bitmap.isNull());
 
-    std::unique_ptr<SkCanvas> canvas(new SkCanvas(bitmap));
+    sk_sp<SkCanvas> canvas(new SkCanvas(bitmap));
 
     // setup the matrix and clip
     setup_canvas_from_MC_state(layerState.mcState, canvas.get());
 
-    return canvas;
+    return canvas.release();
 }
 
-std::unique_ptr<SkCanvas> SkCanvasStateUtils::MakeFromCanvasState(const SkCanvasState* state) {
+SkCanvas* SkCanvasStateUtils::CreateFromCanvasState(const SkCanvasState* state) {
     SkASSERT(state);
     // Currently there is only one possible version.
     SkASSERT(SkCanvasState_v1::kVersion == state->version);
@@ -318,14 +323,14 @@ std::unique_ptr<SkCanvas> SkCanvasStateUtils::MakeFromCanvasState(const SkCanvas
         return nullptr;
     }
 
-    std::unique_ptr<SkCanvasStack> canvas(new SkCanvasStack(state->width, state->height));
+    sk_sp<SkCanvasStack> canvas(new SkCanvasStack(state->width, state->height));
 
     // setup the matrix and clip on the n-way canvas
     setup_canvas_from_MC_state(state_v1->mcState, canvas.get());
 
     // Iterate over the layers and add them to the n-way canvas
     for (int i = state_v1->layerCount - 1; i >= 0; --i) {
-        std::unique_ptr<SkCanvas> canvasLayer = make_canvas_from_canvas_layer(state_v1->layers[i]);
+        sk_sp<SkCanvas> canvasLayer(create_canvas_from_canvas_layer(state_v1->layers[i]));
         if (!canvasLayer.get()) {
             return nullptr;
         }
@@ -333,7 +338,7 @@ std::unique_ptr<SkCanvas> SkCanvasStateUtils::MakeFromCanvasState(const SkCanvas
                                                              state_v1->layers[i].y));
     }
 
-    return std::move(canvas);
+    return canvas.release();
 }
 
 ////////////////////////////////////////////////////////////////////////////////