Revert "disable passing discards through GrIODB."

This reverts commit 3cdd1460991b723521be8b7c26e808e640402b7e.

The original CL was landed only to do an experimental DEPS roll to Chromium.

BUG=skia:

Review URL: https://codereview.chromium.org/219023008

git-svn-id: http://skia.googlecode.com/svn/trunk@13995 2bbb7eff-a529-9590-31e7-b0007b416f81

src/gpu/GrInOrderDrawBuffer.cpp

@@ -645,7 +645,7 @@ void GrInOrderDrawBuffer::flush() {
                 ++currClip;
                 break;
             case kClear_Cmd:
-                if (false && GrColor_ILLEGAL == fClears[currClear].fColor) {
+                if (GrColor_ILLEGAL == fClears[currClear].fColor) {
                     fDstGpu->discard(fClears[currClear].fRenderTarget);
                 } else {
                     fDstGpu->clear(&fClears[currClear].fRect,