Added FBO Invalidation workaround for Nexus 6.

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 0886768193444d6e61c7467c5ef30e28aeaf85a6..03f65f69cc97c3c927081fe930f8eb2478bddb29 100644
--- a/gpu/command_buffer/service/gles2_cmd_decoder.cc
+++ b/gpu/command_buffer/service/gles2_cmd_decoder.cc
@@ -4492,6 +4492,9 @@ void GLES2DecoderImpl::DoDisableVertexAttribArray(GLuint index) {
 void GLES2DecoderImpl::DoDiscardFramebufferEXT(GLenum target,
                                                GLsizei numAttachments,
                                                const GLenum* attachments) {
+  if (workarounds().disable_fbo_invalidations)
+    return;
+
   Framebuffer* framebuffer =
       GetFramebufferInfoForTarget(GL_FRAMEBUFFER);