Simplify platform_canvas.h by recognizing that PlatformCanvas does not actually extend

skia/ext/bitmap_platform_device_mac.cc

Index: skia/ext/bitmap_platform_device_mac.cc
===================================================================
--- skia/ext/bitmap_platform_device_mac.cc	(revision 167659)
+++ skia/ext/bitmap_platform_device_mac.cc	(working copy)
@@ -28,6 +28,12 @@
 #if defined(SK_CPU_LENDIAN) && HAS_ARGB_SHIFTS(24, 16, 8, 0)
   // Allocate a bitmap context with 4 components per pixel (BGRA).  Apple
   // recommends these flags for improved CG performance.
+
+  // CGBitmapContextCreate returns NULL if width/height are 0. However, our
+  // callers expect to get a canvas back (which they later resize/reallocate)
+  // so we pin the dimensions here.
+  width = SkMax32(1, width);
+  height = SkMax32(1, height);
   CGContextRef context =
       CGBitmapContextCreate(data, width, height, 8, width * 4,
                             base::mac::GetSystemColorSpace(),
@@ -255,6 +261,21 @@
   return bitmap_device;
 }
 
+// PlatformCanvas impl
+
+SkCanvas* CreatePlatformCanvas(CGContextRef ctx, int width, int height,
+                               bool is_opaque, OnFailureType failureType) {
+  SkDevice* dev = BitmapPlatformDevice::Create(ctx, width, height, is_opaque);
+  return CreateCanvas(dev, failureType);
+}
+
+SkCanvas* CreatePlatformCanvas(int width, int height, bool is_opaque,
+                               uint8_t* data, OnFailureType failureType) {
+  SkDevice* dev = BitmapPlatformDevice::CreateWithData(data, width, height,
+                                                       is_opaque);
+  return CreateCanvas(dev, failureType);
+}
+
 // Port of PlatformBitmap to mac
 
 PlatformBitmap::~PlatformBitmap() {