Enable asynchronous glReadPixels on Windows.

gpu/command_buffer/service/gles2_cmd_decoder.cc

Index: gpu/command_buffer/service/gles2_cmd_decoder.cc
diff --git a/gpu/command_buffer/service/gles2_cmd_decoder.cc b/gpu/command_buffer/service/gles2_cmd_decoder.cc
index c7fab686353c00671275af1f55d6f70938779f3e..1b48dd760ffad53f65393a26f9a4475a934c410d 100644
--- a/gpu/command_buffer/service/gles2_cmd_decoder.cc
+++ b/gpu/command_buffer/service/gles2_cmd_decoder.cc
@@ -7550,12 +7550,15 @@ void GLES2DecoderImpl::FinishReadPixels(
     } else {
       data = glMapBuffer(GL_PIXEL_PACK_BUFFER_ARB, GL_READ_ONLY);
     }
-    memcpy(pixels, data, pixels_size);
+    if (data)

[piman, 2014/11/11 22:54:31]

In which case should data be NULL?
Should we raise GL_OUT_OF_MEMORY, or lose the context if that's the case?

Silently failing seems bad.

+      memcpy(pixels, data, pixels_size);
     // GL_PIXEL_PACK_BUFFER_ARB is currently unused, so we don't
     // have to restore the state.
     glUnmapBuffer(GL_PIXEL_PACK_BUFFER_ARB);
     glBindBuffer(GL_PIXEL_PACK_BUFFER_ARB, 0);
     glDeleteBuffersARB(1, &buffer);
+    if (!data)
+      return;
   }
 
   if (result != NULL) {
@@ -7751,7 +7754,10 @@ error::Error GLES2DecoderImpl::HandleReadPixels(uint32 immediate_data_size,
       GLuint buffer = 0;
       glGenBuffersARB(1, &buffer);
       glBindBuffer(GL_PIXEL_PACK_BUFFER_ARB, buffer);
-      glBufferData(GL_PIXEL_PACK_BUFFER_ARB, pixels_size, NULL, GL_STREAM_READ);
+      // For ANGLE client version 2, GL_STREAM_READ is not available.
+      const GLenum usage_hint =
+          features().is_angle ? GL_STATIC_DRAW : GL_STREAM_READ;
+      glBufferData(GL_PIXEL_PACK_BUFFER_ARB, pixels_size, NULL, usage_hint);
       GLenum error = glGetError();
       if (error == GL_NO_ERROR) {
         glReadPixels(x, y, width, height, format, type, 0);