SetPermitSubpixelAA for capture draw targets based on mFormat (bug 1422392, r=nical)

Other draw targets do this in their initialization code, so capture should also.
MozReview-Commit-ID: CBsui9IJwXI

--HG--
extra : rebase_source : c3a818618cee0bab7ac3c99a42daf698c063e0c0

gfx/2d/DrawTargetCapture.cpp

@@ -34,6 +34,7 @@ DrawTargetCaptureImpl::DrawTargetCaptureImpl(BackendType aBackend,
       gfxPlatform::GetPlatform()->ScreenReferenceDrawTarget();
 
   mFormat = aFormat;
+  SetPermitSubpixelAA(IsOpaque(mFormat));
   if (aBackend == screenRefDT->GetBackendType()) {
     mRefDT = screenRefDT;
   } else {
@@ -66,6 +67,7 @@ DrawTargetCaptureImpl::Init(const IntSize& aSize, DrawTarget* aRefDT)
 
   mSize = aSize;
   mFormat = aRefDT->GetFormat();
+  SetPermitSubpixelAA(IsOpaque(mFormat));
   return true;
 }