Add UMA to estimate deroppable memory usage of encoded data size in Resources

third_party/WebKit/Source/core/fetch/ImageResource.cpp

Index: third_party/WebKit/Source/core/fetch/ImageResource.cpp
diff --git a/third_party/WebKit/Source/core/fetch/ImageResource.cpp b/third_party/WebKit/Source/core/fetch/ImageResource.cpp
index 929cb375d24e5dcb1ae3a954288a0506d43996ba..c8cf194774c5b9e9b830aab7ab231d972b4c2792 100644
--- a/third_party/WebKit/Source/core/fetch/ImageResource.cpp
+++ b/third_party/WebKit/Source/core/fetch/ImageResource.cpp
@@ -23,6 +23,7 @@
 
 #include "core/fetch/ImageResource.h"
 
+#include "base/metrics/histogram_macros.h"
 #include "core/fetch/ImageResourceObserver.h"
 #include "core/fetch/MemoryCache.h"
 #include "core/fetch/ResourceClient.h"
@@ -252,6 +253,10 @@ void ImageResource::destroyDecodedDataIfPossible() {
     return;
   CHECK(!errorOccurred());
   m_image->destroyDecodedData();
+  if (!isPreloaded() && isReloadable()) {
+    UMA_HISTOGRAM_MEMORY_KB("Memory.Renderer.EstimantedDroppableEncodedSize",
+                            encodedSize() / 1024);
+  }
 }
 
 void ImageResource::doResetAnimation() {