Make SkImageFilter methods const.

src/effects/SkTestImageFilters.cpp

 
 #include "SkTestImageFilters.h"
 #include "SkCanvas.h"
 #include "SkDevice.h"
 #include "SkReadBuffer.h"
 #include "SkWriteBuffer.h"
 
 // Simple helper canvas that "takes ownership" of the provided device, so that
 // when this canvas goes out of scope, so will its device. Could be replaced
 // with the following:
 //
 //  SkCanvas canvas(device);
 //  SkAutoTUnref<SkBaseDevice> aur(device);
 //
 class OwnDeviceCanvas : public SkCanvas {
 public:
     OwnDeviceCanvas(SkBaseDevice* device) : SkCanvas(device) {
         SkSafeUnref(device);
     }
 };
 
 ///////////////////////////////////////////////////////////////////////////////
 
 bool SkDownSampleImageFilter::onFilterImage(Proxy* proxy, const SkBitmap& src,
                                             const SkMatrix&,
-                                            SkBitmap* result, SkIPoint*) {
+                                            SkBitmap* result, SkIPoint*) const {
     SkScalar scale = fScale;
     if (scale > SK_Scalar1 || scale <= 0) {
         return false;
     }
 
     int dstW = SkScalarRoundToInt(src.width() * scale);
     int dstH = SkScalarRoundToInt(src.height() * scale);
     if (dstW < 1) {
         dstW = 1;
     }
@@ skipping 38 matching lines @@
     this->INHERITED::flatten(buffer);
 
     buffer.writeScalar(fScale);
 }
 
 SkDownSampleImageFilter::SkDownSampleImageFilter(SkReadBuffer& buffer)
   : INHERITED(1, buffer) {
     fScale = buffer.readScalar();
     buffer.validate(SkScalarIsFinite(fScale));
 }