Make sure SkDrawLooper objects can only be allocated on the heap.

Make constructors of SkLayerDrawLooper and SkBlurDrawLooper non-public.
Remove addLayer* methods from SkLayerDrawLooper. SkLayerDrawLooper::Builder is
used to create new objects.
Provide factory method for creating SkBlurDrawLooper.

BUG=2141
R=scroggo@google.com, reed@google.com, djsollen@google.com

Author: dominikg@chromium.org

Review URL: https://codereview.chromium.org/232913003

git-svn-id: http://skia.googlecode.com/svn/trunk@14200 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/src/effects/SkBlurDrawLooper.cpp b/src/effects/SkBlurDrawLooper.cpp
index 2caa62e..5cfb8d8 100644
--- a/src/effects/SkBlurDrawLooper.cpp
+++ b/src/effects/SkBlurDrawLooper.cpp
@@ -17,10 +17,12 @@
 #include "SkString.h"
 #include "SkStringUtils.h"
 
+#ifdef SK_SUPPORT_LEGACY_BLURDRAWLOOPERCONSTRUCTORS
 SkBlurDrawLooper::SkBlurDrawLooper(SkScalar radius, SkScalar dx, SkScalar dy,
                                    SkColor color, uint32_t flags) {
     this->init(SkBlurMask::ConvertRadiusToSigma(radius), dx, dy, color, flags);
 }
+#endif
 
 SkBlurDrawLooper::SkBlurDrawLooper(SkColor color, SkScalar sigma,
                                    SkScalar dx, SkScalar dy, uint32_t flags) {