Fixing compile error on OS X with 10.3.9 SDK. r=vlad.

content/canvas/src/nsCanvasRenderingContext2D.cpp

@@ -931,7 +931,7 @@ nsCanvasRenderingContext2D::Render(nsIRenderingContext *rc)
                                                  NULL);
     CGColorSpaceRef rgb = CGColorSpaceCreateDeviceRGB();
     img = CGImageCreate (mWidth, mHeight, 8, 32, mWidth * 4, rgb,
-                         kCGImageAlphaPremultipliedFirst | kCGBitmapByteOrder32Host,
+                         (CGImageAlphaInfo)(kCGImageAlphaPremultipliedFirst | kCGBitmapByteOrder32Host),
                          dataProvider, NULL, false, kCGRenderingIntentDefault);
     CGColorSpaceRelease (rgb);
     CGDataProviderRelease (dataProvider);