[Doodle] Add UMA for doodle image downloads

tools/metrics/histograms/histograms.xml

Index: tools/metrics/histograms/histograms.xml
diff --git a/tools/metrics/histograms/histograms.xml b/tools/metrics/histograms/histograms.xml
index f0f3f9a4f7160f894dbbf81a4b9657cb96408027..30d1e8f6b305ddca430501e40349bffaed98cd7b 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -41207,6 +41207,14 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="NewTabPage.LogoImageDownloaded" enum="BooleanFromHTTPCache">
+  <owner>treib@chromium.org</owner>
+  <summary>
+    A logo image (static or CTA) was downloaded. Recorded only when the image
+    was downloaded and decoded without errors.
+  </summary>
+</histogram>
+
 <histogram name="NewTabPage.LogoShown" enum="NewTabPageLogoShown">
   <owner>ianwen@chromium.org</owner>
   <summary>
@@ -83143,6 +83151,11 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <int value="1" label="From Address Book"/>
 </enum>
 
+<enum name="BooleanFromHTTPCache" type="int">
+  <int value="0" label="Downloaded from network"/>
+  <int value="1" label="HTTP cache hit"/>
+</enum>
+
 <enum name="BooleanGAIAWebViewFlow" type="int">
   <int value="0" label="iframe-based flow"/>
   <int value="1" label="WebView-based flow"/>