Move canvas->surface association to the device subclasses

src/core/SkBitmapDevice.cpp

Index: src/core/SkBitmapDevice.cpp
diff --git a/src/core/SkBitmapDevice.cpp b/src/core/SkBitmapDevice.cpp
index 1f17e6fac12d30212f62819c75cd6fa47b6986ea..f902e59f72fe625851c3c3cfad1bf9502a08b7e9 100644
--- a/src/core/SkBitmapDevice.cpp
+++ b/src/core/SkBitmapDevice.cpp
@@ -69,11 +69,10 @@ SkBitmapDevice::SkBitmapDevice(const SkBitmap& bitmap, const SkDeviceProperties&
     SkASSERT(valid_for_bitmap_device(bitmap.info(), NULL));
 }
 
-SkBitmapDevice* SkBitmapDevice::Create(const SkImageInfo& origInfo,
-                                       const SkDeviceProperties* props) {
+bool SkBitmapDevice::CreateBackendBitmap(const SkImageInfo& origInfo, SkBitmap* target) {
     SkAlphaType newAT = origInfo.alphaType();
     if (!valid_for_bitmap_device(origInfo, &newAT)) {
-        return NULL;
+        return false;
     }
 
     const SkImageInfo info = origInfo.makeAlphaType(newAT);
@@ -81,17 +80,26 @@ SkBitmapDevice* SkBitmapDevice::Create(const SkImageInfo& origInfo,
 
     if (kUnknown_SkColorType == info.colorType()) {
         if (!bitmap.setInfo(info)) {
-            return NULL;
+            return false;
         }
     } else {
         if (!bitmap.tryAllocPixels(info)) {
-            return NULL;
+            return false;
         }
         if (!bitmap.info().isOpaque()) {
             bitmap.eraseColor(SK_ColorTRANSPARENT);
         }
     }
+    target->swap(bitmap);
+    return true;
+}
 
+SkBitmapDevice* SkBitmapDevice::Create(const SkImageInfo& info,
+                                       const SkDeviceProperties* props) {
+    SkBitmap bitmap;
+    if (!CreateBackendBitmap(info, &bitmap)) {
+        return NULL;
+    }
     if (props) {
         return SkNEW_ARGS(SkBitmapDevice, (bitmap, *props));
     } else {
@@ -103,7 +111,7 @@ SkImageInfo SkBitmapDevice::imageInfo() const {
     return fBitmap.info();
 }
 
-void SkBitmapDevice::replaceBitmapBackendForRasterSurface(const SkBitmap& bm) {
+void SkBitmapDevice::replaceBitmapBackend(const SkBitmap& bm) {
     SkASSERT(bm.width() == fBitmap.width());
     SkASSERT(bm.height() == fBitmap.height());
     fBitmap = bm;   // intent is to use bm's pixelRef (and rowbytes/config)