Add convenience function on GrDrawState to set state bit based on a bool.

R=robertphillips@google.com
Review URL: https://codereview.appspot.com/6615044

git-svn-id: http://skia.googlecode.com/svn/trunk@5815 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/src/gpu/GrClipMaskManager.cpp b/src/gpu/GrClipMaskManager.cpp
index 5ca714a..f40c265 100644
--- a/src/gpu/GrClipMaskManager.cpp
+++ b/src/gpu/GrClipMaskManager.cpp
@@ -785,11 +785,7 @@
             drawState->disableState(GrGpu::kModifyStencilClip_StateBit);
             // if the target is MSAA then we want MSAA enabled when the clip is soft
             if (rt->isMultisampled()) {
-                if (clip->fDoAA) {
-                    drawState->enableState(GrDrawState::kHWAntialias_StateBit);
-                } else {
-                    drawState->disableState(GrDrawState::kHWAntialias_StateBit);
-                }
+                drawState->setState(GrDrawState::kHWAntialias_StateBit, clip->fDoAA);
             }
 
             // Can the clip element be drawn directly to the stencil buffer