Handle the case when the GrResourceCache timestamp wraps.

src/gpu/GrTest.cpp

Index: src/gpu/GrTest.cpp
diff --git a/src/gpu/GrTest.cpp b/src/gpu/GrTest.cpp
index 0e1c069ac2a8810168f8808b498adfd7d3c4c080..9ddc97d8341828a60df322e14f6942702800ddeb 100644
--- a/src/gpu/GrTest.cpp
+++ b/src/gpu/GrTest.cpp
@@ -125,6 +125,9 @@ void GrResourceCache::dumpStats(SkString* out) const {
 
 #endif
 
+///////////////////////////////////////////////////////////////////////////////
+
+void GrResourceCache::changeTimestamp(uint32_t newTimestamp) { fTimestamp = newTimestamp; }
 
 ///////////////////////////////////////////////////////////////////////////////
 // Code for the mock context. It's built on a mock GrGpu class that does nothing.