Fix a misuse of framebuffer target in GLHelper.

content/common/gpu/client/gl_helper.cc

Index: content/common/gpu/client/gl_helper.cc
diff --git a/content/common/gpu/client/gl_helper.cc b/content/common/gpu/client/gl_helper.cc
index f28be72dab2c25d148a5af4903147808ed26a9a8..0d594ece3e321c8cefd91b87dc452e5c3661c40c 100644
--- a/content/common/gpu/client/gl_helper.cc
+++ b/content/common/gpu/client/gl_helper.cc
@@ -547,11 +547,11 @@ void GLHelper::CopyTextureToImpl::ReadBackFramebuffer(
     size = request->size;
     {
       ScopedFlush flush(context);
-      ScopedFramebufferBinder<GL_DRAW_FRAMEBUFFER> framebuffer_binder(
+      ScopedFramebufferBinder<GL_READ_FRAMEBUFFER> framebuffer_binder(
           context, dst_framebuffer);
       ScopedTextureBinder<GL_TEXTURE_2D> texture_binder(
           context, request->texture);
-      context->framebufferTexture2D(GL_DRAW_FRAMEBUFFER,
+      context->framebufferTexture2D(GL_READ_FRAMEBUFFER,
                                     GL_COLOR_ATTACHMENT0,
                                     GL_TEXTURE_2D,
                                     request->texture,