Zero out GrSamplerState in constructor to recover performance loss on Linux from r4102.

(Noise in padding bytes was breaking operator==())
Visual review by bsalomon@.



git-svn-id: http://skia.googlecode.com/svn/trunk@4108 2bbb7eff-a529-9590-31e7-b0007b416f81

include/gpu/GrSamplerState.h

@@ -90,6 +90,7 @@ public:
     , fRadial2Radius0()
     , fRadial2PosRoot()
     , fCustomStage (NULL) {
+        memset(this, 0, sizeof(GrSamplerState));
         this->reset();
     }