Deduplicate unneeded SetTransform and SetPermitSubpixelAA calls from DrawTargetCapture (bug 1431813, r=bas)

--HG--
extra : rebase_source : 30b2051494aa247df922e87779a1f866e1b45e97

gfx/2d/DrawTargetCapture.cpp

@@ -119,6 +119,11 @@ DrawTargetCaptureImpl::DetachAllSnapshots()
 void
 DrawTargetCaptureImpl::SetPermitSubpixelAA(bool aPermitSubpixelAA)
 {
+  // Save memory by eliminating state changes with no effect
+  if (mPermitSubpixelAA == aPermitSubpixelAA) {
+    return;
+  }
+
   AppendCommand(SetPermitSubpixelAACommand)(aPermitSubpixelAA);
 
   // Have to update mPermitSubpixelAA for this DT
@@ -310,6 +315,11 @@ DrawTargetCaptureImpl::PopClip()
 void
 DrawTargetCaptureImpl::SetTransform(const Matrix& aTransform)
 {
+  // Save memory by eliminating state changes with no effect
+  if (mTransform.ExactlyEquals(aTransform)) {
+    return;
+  }
+
   AppendCommand(SetTransformCommand)(aTransform);
 
   // Have to update the transform for this DT