[Mac] Create transparent cursor when given empty custom data.

webkit/glue/webcursor_mac.mm

Index: webkit/glue/webcursor_mac.mm
diff --git a/webkit/glue/webcursor_mac.mm b/webkit/glue/webcursor_mac.mm
index 8c72da206af47101416ae2c25435e43203485bcd..ca9ee0d0b52e70103f1b007cdd787cfdc5e20662 100644
--- a/webkit/glue/webcursor_mac.mm
+++ b/webkit/glue/webcursor_mac.mm
@@ -40,7 +40,9 @@ CGImageRef CreateCGImageFromCustomData(const std::vector<char>& custom_data,
   base::mac::ScopedCFTypeRef<CGColorSpaceRef> cg_color(
       CGColorSpaceCreateDeviceRGB());
   // This is safe since we're not going to draw into the context we're creating.
-  void* data = const_cast<char*>(&custom_data[0]);
+  void* data = NULL;
+  if (!custom_data.empty())
+    data = const_cast<char*>(&custom_data[0]);
   // The settings here match SetCustomData() below; keep in sync.
   base::mac::ScopedCFTypeRef<CGContextRef> context(
       CGBitmapContextCreate(data,

[Avi (use Gerrit), 2011/06/29 00:22:47]

You can do that, pass in a null data for a 0x0 image?

[Scott Hess - ex-Googler, 2011/06/29 01:06:13]

Docs say that passing NULL means that Quartz allocates the memory.

I tested with NULL - but the size was non-zero.  In that case it worked as
expected.  But I just went back and instrumented the code to pass a size of
{0,0}, and in that case CGBitmapContextCreate() returns NULL, and the exception
stuff from the old comment happens.

I tried revising so that |cursor_image| gets no representation in case of NULL
or 0x0, but no go.  Nothing bad happens, but the cursor doesn't change at all. 
The docs seem to imply that a zero-size image is not going to generally work
well, in any case.

I do not have enough insight into the overall system to be able to offhand say
if we can get an actual {0,0} size, or if the empty image data with a non-zero
size is expected.  The transparent cursor seems right, it would be easy enough
to pass NULL for data (system allocated transparent backing) and {1,1} for size
in that case.  Or I could back off and instrument RWHVM further to dump the size
into breakpad along with the type.

[I can't for the life of me figure out how to snag the URL for this crash, that
would rock.]

@@ -57,10 +59,6 @@ CGImageRef CreateCGImageFromCustomData(const std::vector<char>& custom_data,
 NSCursor* CreateCustomCursor(const std::vector<char>& custom_data,
                              const gfx::Size& custom_size,
                              const gfx::Point& hotspot) {
-  // CG throws a cocoa exception if we try to create an empty image, which
-  // results in an infinite loop.  This CHECK ensures that we crash instead.
-  CHECK(!custom_data.empty());
-
   base::mac::ScopedCFTypeRef<CGImageRef> cg_image(
       CreateCGImageFromCustomData(custom_data, custom_size));