Added histogram names to the picture element use counter.

BUG=408797

Review URL: https://codereview.chromium.org/517343003

Cr-Commit-Position: refs/heads/master@{#292788}

tools/metrics/histograms/histograms.xml

@@ -42007,6 +42007,10 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   <int value="518" label="DevToolsConsoleProfile"/>
   <int value="519" label="SVGStyleElementTitle"/>
   <int value="520" label="PictureSourceSrc"/>
+  <int value="521" label="Picture"/>
+  <int value="522" label="Sizes"/>
+  <int value="523" label="SrcsetXDescriptor"/>
+  <int value="524" label="SrcsetWDescriptor"/>
 </enum>
 
 <enum name="FFmpegCodecs" type="int">