Optionally clear PlatformCanvas instances.

skia/ext/bitmap_platform_device_mac.cc

Index: skia/ext/bitmap_platform_device_mac.cc
===================================================================
--- skia/ext/bitmap_platform_device_mac.cc	(revision 123041)
+++ skia/ext/bitmap_platform_device_mac.cc	(working copy)
@@ -113,7 +113,7 @@
 BitmapPlatformDevice* BitmapPlatformDevice::Create(CGContextRef context,
                                                    int width,
                                                    int height,
-                                                   bool is_opaque) {
+                                                   int flags) {
   SkBitmap bitmap;
   bitmap.setConfig(SkBitmap::kARGB_8888_Config, width, height);
   if (bitmap.allocPixels() != true)
@@ -129,14 +129,15 @@
     // Note: The Windows implementation clears the Bitmap later on.
     // This bears mentioning since removal of this line makes the
     // unit tests only fail periodically (or when MallocPreScribble is set).
-    bitmap.eraseARGB(0, 0, 0, 0);
+    if (flags & FLAGS_INITIALIZED)
+      bitmap.eraseARGB(0, 0, 0, 0);
   }
 
-  bitmap.setIsOpaque(is_opaque);
+  bitmap.setIsOpaque(flags & FLAGS_OPAQUE);
 
   // If we were given data, then don't clobber it!
 #ifndef NDEBUG
-  if (!context && is_opaque) {
+  if (!context && (flags & FLAGS_OPAQUE)) {
     // To aid in finding bugs, we set the background color to something
     // obviously wrong so it will be noticable when it is not cleared
     bitmap.eraseARGB(255, 0, 255, 128);  // bright bluish green
@@ -163,12 +164,12 @@
 BitmapPlatformDevice* BitmapPlatformDevice::CreateWithData(uint8_t* data,
                                                            int width,
                                                            int height,
-                                                           bool is_opaque) {
+                                                           int flags) {
   CGContextRef context = NULL;
   if (data)
     context = CGContextForData(data, width, height);
 
-  BitmapPlatformDevice* rv = Create(context, width, height, is_opaque);
+  BitmapPlatformDevice* rv = Create(context, width, height, flags);
 
   // The device object took ownership of the graphics context with its own
   // CGContextRetain call.
@@ -242,7 +243,8 @@
     SkBitmap::Config config, int width, int height, bool isOpaque,
     Usage /*usage*/) {
   SkASSERT(config == SkBitmap::kARGB_8888_Config);
-  return BitmapPlatformDevice::Create(NULL, width, height, isOpaque);
+  return BitmapPlatformDevice::Create(NULL, width, height,
+                                      GetDefaultFlags(isOpaque));
 }
 
 }  // namespace skia