Linux Skia: add an option to build a canvas from a provided memory buffer

skia/ext/platform_canvas_linux.cc

Index: skia/ext/platform_canvas_linux.cc
diff --git a/skia/ext/platform_canvas_linux.cc b/skia/ext/platform_canvas_linux.cc
index 5c14707701806d73249df57bf08b0a45b4605ba9..d436fd765c2784788d7fb64e0f811b72d4144774 100644
--- a/skia/ext/platform_canvas_linux.cc
+++ b/skia/ext/platform_canvas_linux.cc
@@ -8,6 +8,8 @@
 #include "skia/ext/bitmap_platform_device_linux.h"
 #include "SkTypes.h"
 
+#include <cairo/cairo.h>
+
 namespace skia {
 
 PlatformCanvasLinux::PlatformCanvasLinux() : SkCanvas() {
@@ -52,4 +54,9 @@ SkDevice* PlatformCanvasLinux::createPlatformDevice(int width,
   return BitmapPlatformDeviceLinux::Create(width, height, is_opaque);
 }
 
+// static
+size_t PlatformCanvasLinux::StrideForWidth(unsigned width) {
+  return cairo_format_stride_for_width(CAIRO_FORMAT_ARGB32, width);
+}
+
 }  // namespace skia