Adds UMA histogram metrics for SafeBrowsing PVer4 methods.

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 44b26ef1332cbf1473788f7bbb2ec137772da88d..cbecb450d7b3405e4da0e3259c49a37a6757de68 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -40252,6 +40252,31 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="SafeBrowsing.GetV4HashHttpResponseOrErrorCode"
+    enum="CombinedHttpResponseAndNetErrorCode">
+  <owner>kcarattini@google.com</owner>
+  <summary>
+    Response or error codes from the SafeBrowsing Pver4 service. Logged after a
+    GetHash or request finishes to capture the response code or error code for
+    that call.
+  </summary>
+</histogram>
+
+<histogram name="SafeBrowsing.GetV4HashResult" enum="SB2GetHashResult">
+  <owner>kcarattini@chromium.org</owner>
+  <summary>
+    Track return status from V4 GetHash attempts (STATUS_200, STATUS_204,
+    NETWORK_ERROR, HTTP_ERROR, BACKOFF_ERROR, PARSE_ERROR, NETWORK_ERROR,
+    HTTP_ERROR, BACKOFF_ERROR and MIN_WAIT_DURATION_ERROR), whether parsing a
+    200 result failed (PARSE_ERROR), and dispensation of returned values (EMPTY,
+    HIT, MISS). EMPTY means the response had no full hashes, and should contain
+    all of the 204 responses plus all *_ERROR cases.  HIT means that one of the
+    full hashes matched. MISS means that none of the hashes matched (there was a
+    prefix collision). The buckets of this histogram overlap, so the counts
+    cannot be used as percentages.
+  </summary>
+</histogram>
+
 <histogram name="SafeBrowsing.ModuleBaseRelocation" units="BaseRelocationType">
   <owner>csharp@chromium.org</owner>
   <owner>krstnmnlsn@chromium.org</owner>
@@ -75713,6 +75738,7 @@ To add a new entry, add it with any value and run test to compute valid value.
   <int value="6" label="NETWORK_ERROR"/>
   <int value="7" label="HTTP_ERROR"/>
   <int value="8" label="BACKOFF_ERROR"/>
+  <int value="9" label="MIN_WAIT_DURATION_ERROR"/>
 </enum>
 
 <enum name="SB2InterstitialAction" type="int">