Invalidate GrTexture mipmap on content change notification

src/core/SkPixelRef.cpp

Index: src/core/SkPixelRef.cpp
diff --git a/src/core/SkPixelRef.cpp b/src/core/SkPixelRef.cpp
index 4d6526882070d6decec685e0150127322bf75e1d..cfe93fda5883713144ff51b083a5bda6b26e85f5 100644
--- a/src/core/SkPixelRef.cpp
+++ b/src/core/SkPixelRef.cpp
@@ -335,6 +335,7 @@ void SkPixelRef::notifyPixelsChanged() {
 #endif
     this->callGenIDChangeListeners();
     this->needsNewGenID();
+    this->onNotifyPixelsChanged();
 }
 
 void SkPixelRef::changeAlphaType(SkAlphaType at) {
@@ -355,6 +356,8 @@ bool SkPixelRef::onReadPixels(SkBitmap* dst, const SkIRect* subset) {
     return false;
 }
 
+void SkPixelRef::onNotifyPixelsChanged() { }
+
 SkData* SkPixelRef::onRefEncodedData() {
     return NULL;
 }