Add UMA histograms to AsyncResourceHandler to track content size.

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 78a0d5c2e7dc58675eccfbc51a9fbf4bfedf9dcd..d55ad23f909862df9a17ca616a5e05b56ef6bafa 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -34744,6 +34744,16 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Net.ResourceLoader.ExpectedContentSizeResult"
+    enum="ResourceLoaderExpectedContentSizeResult">
+  <owner>maksim.sisov@intel.com</owner>
+  <owner>mmenke@chromium.org</owner>
+  <summary>
+    Records how many times expected content size equals/less/more than size of
+    read body/buffer or content size is unkown. Recorded for each resource load.
+  </summary>
+</histogram>
+
 <histogram name="Net.ResourceLoader.InliningStatus"
     enum="ResourceLoaderInliningStatus">
   <owner>tzik@chromium.org</owner>
@@ -102936,6 +102946,15 @@ value.
   <int value="1" label="Has client"/>
 </enum>
 
+<enum name="ResourceLoaderExpectedContentSizeResult" type="int">
+  <int value="0" label="EQ_RESPONSE_BODY"/>
+  <int value="1" label="EQ_RESPONSE_BODY_GT_EQ_BUFFER_SIZE"/>
+  <int value="2" label="GT_EQ_BUFFER_SIZE"/>
+  <int value="3" label="LT_RESPONSE_BODY"/>
+  <int value="4" label="GT_RESPONSE_BODY"/>
+  <int value="5" label="UNKNOWN"/>
+</enum>
+
 <enum name="ResourceLoaderInliningStatus" type="int">
   <int value="0" label="Applicable"/>
   <int value="1" label="EarlyAllocation"/>