Add f suffix to 0.5 to fix mac 10.6 warning

src/gpu/effects/GrRRectEffect.cpp

Index: src/gpu/effects/GrRRectEffect.cpp
diff --git a/src/gpu/effects/GrRRectEffect.cpp b/src/gpu/effects/GrRRectEffect.cpp
index a2a6af7924881f6c0d29bd6466cbdd76caa92ac1..3923a6f36bc2e76fe82101b2973b6067b1eb3e53 100644
--- a/src/gpu/effects/GrRRectEffect.cpp
+++ b/src/gpu/effects/GrRRectEffect.cpp
@@ -15,7 +15,7 @@
 
 // This effect only supports circular corner rrects where all corners have the same radius
 // which must be <= kRadiusMin.
-static const SkScalar kRadiusMin = 0.5;
+static const SkScalar kRadiusMin = 0.5f;
 
 //////////////////////////////////////////////////////////////////////////////
 class GrGLRRectEffect : public GrGLEffect {