Update GPU memory buffers to use StrideInBytes internally.

ui/gl/gl_image_shared_memory.cc

Index: ui/gl/gl_image_shared_memory.cc
diff --git a/ui/gl/gl_image_shared_memory.cc b/ui/gl/gl_image_shared_memory.cc
index 0bbf54910fcc9c9fe7391954f8c9adcb1e8434c5..866e24479ed6c8f594b2610fe2e4e7d99a78a271 100644
--- a/ui/gl/gl_image_shared_memory.cc
+++ b/ui/gl/gl_image_shared_memory.cc
@@ -17,9 +17,11 @@ bool SizeInBytes(const gfx::Size& size,
                  size_t* size_in_bytes) {
   if (size.IsEmpty())
     return false;
-  base::CheckedNumeric<size_t> s = GLImageMemory::BytesPerPixel(format);
+  DCHECK_EQ(size.GetArea() * GLImageMemory::BitsPerPixel(format) % 8, 0u);

[reveman, 2014/12/15 17:33:34]

Hm, so this will fail for a 1x1 buffer with bpp < 8. Is that what we want? Are
not all buffer sizes support with compressed formats? In that case, how are we
protecting against a malicious renderer using an invalid size and causing
undefined behavior on the browser or GPU process side? 

[christiank, 2014/12/16 12:02:52]

Currently we don't support images with a width and height not evenly dividable
by 4 so yes, under that premise we expect this to fail.

We try to avoid this by never compressing images that don't meet the criteria.
We currently have checks for this in the tile manager. However, that doesn't
protect us against a malicious renderer. Maybe a CHECK is more appropriate here?

[reveman, 2014/12/16 16:40:12]

A renderer should not be able cause the GPU service to crash. I think if you
replace GLImageMemory::BitsPerPixel with GLImageMemory::StrideInBytes the
problem will just go away as Map() will fail if size/format combination is
invalid.

+  base::CheckedNumeric<size_t> s = GLImageMemory::BitsPerPixel(format);
   s *= size.width();
   s *= size.height();
+  s /= 8;
   if (!s.IsValid())
     return false;
   *size_in_bytes = s.ValueOrDie();