Enable glReadPixels from <video> to 2d context on Android.

content/renderer/media/renderer_gpu_video_accelerator_factories.cc

Index: content/renderer/media/renderer_gpu_video_accelerator_factories.cc
diff --git a/content/renderer/media/renderer_gpu_video_accelerator_factories.cc b/content/renderer/media/renderer_gpu_video_accelerator_factories.cc
index 86d40cd960b67deb86d3dc954cd3c8d96bb6a687..7b4777c03451e87d2fe4d9611508b8f16a8239c1 100644
--- a/content/renderer/media/renderer_gpu_video_accelerator_factories.cc
+++ b/content/renderer/media/renderer_gpu_video_accelerator_factories.cc
@@ -257,11 +257,20 @@ void RendererGpuVideoAcceleratorFactories::AsyncReadPixels(
   gles2->FramebufferTexture2D(
       GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, tmp_texture, 0);
   gles2->PixelStorei(GL_PACK_ALIGNMENT, 4);
+#if SK_B32_SHIFT == 0 && SK_G32_SHIFT == 8 && SK_R32_SHIFT == 16 && \

[scherkus (not reviewing), 2013/10/22 18:29:10]

it seems like the cool kids only check for SK_B32_SHIFT being either 0 or 16
e.g., 
https://code.google.com/p/chromium/codesearch#chromium/src/cc/resources/platf...
https://code.google.com/p/chromium/codesearch#chromium/src/third_party/WebKit...

I guess you're being overly paranoid but there really isn't a reason to check
all four colour components, unless you value saving whitespace

[scherkus (not reviewing), 2013/10/22 18:29:46]

... there really isn't a reason *NOT* to check ...

[Ami GONE FROM CHROMIUM, 2013/10/22 18:32:59]

Yeah, the first version of this code was actually just
#if ANDROID
  use RGBA
#else
  use BGRA_EXT
#endif
but then realized that skia doesn't actually guarantee this, so decided to stay
safe.  When skia doco's that the above logic is correct then I'm fine reverting
to it, but until then planning to leave as-is.

(Skia's naming of ARGB_8888 has confused at least 5 experienced developers re:
this code, including me _twice_ over the last year or two, so opting for extra
explicitness)

+    SK_A32_SHIFT == 24
+  GLenum skia_format = GL_BGRA_EXT;
+#elif SK_R32_SHIFT == 0 && SK_G32_SHIFT == 8 && SK_B32_SHIFT == 16 && \
+    SK_A32_SHIFT == 24
+  GLenum skia_format = GL_RGBA;
+#else
+#error Unexpected Skia ARGB_8888 layout!
+#endif
   gles2->ReadPixels(0,
                     0,
                     size.width(),
                     size.height(),
-                    GL_BGRA_EXT,
+                    skia_format,
                     GL_UNSIGNED_BYTE,
                     read_pixels_bitmap_.pixelRef()->pixels());
   gles2->DeleteFramebuffers(1, &fb);