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

content/renderer/media/renderer_gpu_video_accelerator_factories.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/renderer/media/renderer_gpu_video_accelerator_factories.h"
 
 #include <GLES2/gl2.h>
 #include <GLES2/gl2ext.h>
 
 #include "base/bind.h"
@@ skipping 239 matching lines @@
   gles2->TexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
   context->copyTextureCHROMIUM(
       GL_TEXTURE_2D, texture_id, tmp_texture, 0, GL_RGBA, GL_UNSIGNED_BYTE);
 
   GLuint fb;
   gles2->GenFramebuffers(1, &fb);
   gles2->BindFramebuffer(GL_FRAMEBUFFER, fb);
   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);
   gles2->DeleteTextures(1, &tmp_texture);
   DCHECK_EQ(gles2->GetError(), static_cast<GLenum>(GL_NO_ERROR));
   message_loop_async_waiter_.Signal();
 }
 
 base::SharedMemory* RendererGpuVideoAcceleratorFactories::CreateSharedMemory(
     size_t size) {
@@ skipping 24 matching lines @@
 }
 
 void
 RendererGpuVideoAcceleratorFactories::AsyncDestroyVideoDecodeAccelerator() {
   // OK to release because Destroy() will delete the VDA instance.
   if (vda_)
     vda_.release()->Destroy();
 }
 
 }  // namespace content