Add UMA metrics for the time it takes to read store from disk and apply update

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 e4e29aeeb7dda960671391a639ab42e29e5de9e1..4b36aa9d9058b2e96bab0c35380197c1dd346e24 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -50717,6 +50717,14 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="SafeBrowsing.V4AddUnlumpedHashesTime" units="ms">
+  <owner>vakh@chromium.org</owner>
+  <summary>
+    Records the time it takes to copy the SafeBrowsing list update as a string,
+    into a map.
+  </summary>
+</histogram>
+
 <histogram name="SafeBrowsing.V4ApplyUpdateResult"
     enum="SafeBrowsingV4ApplyUpdateResult">
   <owner>vakh@chromium.org</owner>
@@ -50745,6 +50753,14 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="SafeBrowsing.V4DecodeAdditionsTime" units="ms">
+  <owner>vakh@chromium.org</owner>
+  <summary>
+    Records the time it takes to decode the Rice-encoded additions to the
+    blacklist into raw format.
+  </summary>
+</histogram>
+
 <histogram name="SafeBrowsing.V4DecodeRemovalsResult"
     enum="SafeBrowsingV4DecodeResult">
   <owner>vakh@chromium.org</owner>
@@ -50755,6 +50771,14 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="SafeBrowsing.V4DecodeRemovalsTime" units="ms">
+  <owner>vakh@chromium.org</owner>
+  <summary>
+    Records the time it takes to decode the Rice-encoded removals from the
+    blacklist into raw format.
+  </summary>
+</histogram>
+
 <histogram name="SafeBrowsing.V4FullHashCacheResult"
     enum="SafeBrowsingV4FullHashCacheResult">
   <owner>kcarattini@chromium.org</owner>
@@ -50769,6 +50793,43 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <summary>Track get hash response hits for V4 full hash requests.</summary>
 </histogram>
 
+<histogram name="SafeBrowsing.V4MergeUpdateTime" units="ms">
+  <owner>vakh@chromium.org</owner>
+  <summary>

[Nathan Parker, 2016/09/30 22:32:05]

Can you annotate each of these for cases where one includes another one? It's
not obvious from the descriptions

[vakh (use Gerrit instead), 2016/10/03 21:30:36]

Done.

+    Records the time it takes to merge the existing state of the list with the
+    update. The update may have been received from the server, or it may be the
+    case of reading the store from disk on start-up.

[Nathan Parker, 2016/09/30 22:32:05]

"...or it may have just been read from disk."

[vakh (use Gerrit instead), 2016/10/03 21:30:36]

Done.

+  </summary>
+</histogram>
+
+<histogram name="SafeBrowsing.V4ProcessFullUpdateTime" units="ms">
+  <owner>vakh@chromium.org</owner>
+  <summary>
+    Records the time it takes to process a SafeBrowsing list full update. This
+    may involve decoding some Rice-encoded hash prefixes. It includes the time
+    it takes to convert the update into a hash map that's looked up on resource

[Nathan Parker, 2016/09/30 22:32:05]

what is looked up on resource reputation requests?  I don't understand that
part. Same below.

[vakh (use Gerrit instead), 2016/10/03 21:30:36]

Done. PLMK if the new description is also not clear.

+    reputation requests.
+  </summary>
+</histogram>
+
+<histogram name="SafeBrowsing.V4ProcessPartialUpdateTime" units="ms">
+  <owner>vakh@chromium.org</owner>
+  <summary>
+    Records the time it takes to process a SafeBrowsing list partial update.
+    This may involve decoding some Rice-encoded hash prefixes. It includes the
+    time it takes to merge the update into the hash map that's looked up on
+    resource reputation requests.
+  </summary>
+</histogram>
+
+<histogram name="SafeBrowsing.V4ReadFromDiskTime" units="ms">
+  <owner>vakh@chromium.org</owner>
+  <summary>
+    Records the time it takes to read, parse, and process a SafeBrowsing list
+    stored on disk. This happens at Chromium start-up.
+  </summary>
+</histogram>
+
 <histogram name="SafeBrowsing.V4StoreReadResult"
     enum="SafeBrowsingV4StoreReadResult">
   <owner>vakh@chromium.org</owner>