purge imagefilter cache so we can better track leaks

src/core/SkResourceCache.cpp

Index: src/core/SkResourceCache.cpp
diff --git a/src/core/SkResourceCache.cpp b/src/core/SkResourceCache.cpp
index 0fdb54b191d91ba9eabb9f01df296b38b807d9a2..efe55b48381ebd6432f6c360b5cd7c045cad1803 100644
--- a/src/core/SkResourceCache.cpp
+++ b/src/core/SkResourceCache.cpp
@@ -618,6 +618,7 @@ void SkResourceCache::PostPurgeSharedID(uint64_t sharedID) {
 ///////////////////////////////////////////////////////////////////////////////
 
 #include "SkGraphics.h"
+#include "SkImageFilter.h"
 
 size_t SkGraphics::GetResourceCacheTotalBytesUsed() {
     return SkResourceCache::GetTotalBytesUsed();
@@ -640,6 +641,7 @@ size_t SkGraphics::SetResourceCacheSingleAllocationByteLimit(size_t newLimit) {
 }
 
 void SkGraphics::PurgeResourceCache() {
+    SkImageFilter::PurgeCache();
     return SkResourceCache::PurgeAll();
 }