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, 6 insertions, 13 deletions

diff --git a/src/utils/SkLua.cpp b/src/utils/SkLua.cpp
index 27127df6a8..a2234565cb 100644
--- a/src/utils/SkLua.cpp
+++ b/src/utils/SkLua.cpp
@@ -73,13 +73,6 @@ template <typename T> void push_obj(lua_State* L, const T& obj) {
     lua_setmetatable(L, -2);
 }
 
-template <typename T> T* push_ptr(lua_State* L, T* ptr) {
-    *(T**)lua_newuserdata(L, sizeof(T*)) = ptr;
-    luaL_getmetatable(L, get_mtname<T>());
-    lua_setmetatable(L, -2);
-    return ptr;
-}
-
 template <typename T> T* push_ref(lua_State* L, T* ref) {
     *(T**)lua_newuserdata(L, sizeof(T*)) = SkSafeRef(ref);
     luaL_getmetatable(L, get_mtname<T>());
@@ -340,7 +333,7 @@ void SkLua::pushPath(const SkPath& path, const char key[]) {
 }
 
 void SkLua::pushCanvas(SkCanvas* canvas, const char key[]) {
-    push_ptr(fL, canvas);
+    push_ref(fL, canvas);
     CHECK_SETFIELD(key);
 }
 
@@ -722,7 +715,7 @@ static int lcanvas_newSurface(lua_State* L) {
 }
 
 static int lcanvas_gc(lua_State* L) {
-    // don't know how to track a ptr...
+    get_ref<SkCanvas>(L, 1)->unref();
     return 0;
 }
 
@@ -764,7 +757,7 @@ const struct luaL_Reg gSkCanvas_Methods[] = {
 
 static int ldocument_beginPage(lua_State* L) {
     const SkRect* contentPtr = nullptr;
-    push_ptr(L, get_ref<SkDocument>(L, 1)->beginPage(lua2scalar(L, 2),
+    push_ref(L, get_ref<SkDocument>(L, 1)->beginPage(lua2scalar(L, 2),
                                                      lua2scalar(L, 3),
                                                      contentPtr));
     return 1;
@@ -1757,7 +1750,7 @@ static int lsurface_getCanvas(lua_State* L) {
     if (nullptr == canvas) {
         lua_pushnil(L);
     } else {
-        push_ptr(L, canvas);
+        push_ref(L, canvas);
         // note: we don't unref canvas, since getCanvas did not ref it.
         // warning: this is weird: now Lua owns a ref on this canvas, but what if they let
         // the real owner (the surface) go away, but still hold onto the canvas?
@@ -1821,7 +1814,7 @@ static int lpicturerecorder_beginRecording(lua_State* L) {
         return 1;
     }
 
-    push_ptr(L, canvas);
+    push_ref(L, canvas);
     return 1;
 }
 
@@ -1831,7 +1824,7 @@ static int lpicturerecorder_getCanvas(lua_State* L) {
         lua_pushnil(L);
         return 1;
     }
-    push_ptr(L, canvas);
+    push_ref(L, canvas);
     return 1;
 }