Adds a new UMA histogram to measure the NTP load time since navigation

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 443b3af0ba1586ee176759131684aa17ba32c1aa..3a0ae783297afcd5f92a2c189a6f9a48d1fe4732 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -8879,9 +8879,8 @@ Therefore, the affected-histogram name has to have at least one dot in it.
 <histogram name="Extensions.FeatureProviderStaticInitTime" units="milliseconds">
   <owner>rkaplow@chromium.org</owner>
   <summary>
-    The amount of time that elapsed during
-    extensions::FeatureProvider::Static. Only measured while in the browser
-    process.
+    The amount of time that elapsed during extensions::FeatureProvider::Static.
+    Only measured while in the browser process.
   </summary>
 </histogram>
 
@@ -19591,8 +19590,8 @@ Therefore, the affected-histogram name has to have at least one dot in it.
     enum="QuicSessionLocations">
   <owner>rch@chromium.org</owner>
   <summary>
-    The location in quic_client_session.cc where a session is unexpectedly
-    not going away.
+    The location in quic_client_session.cc where a session is unexpectedly not
+    going away.
   </summary>
 </histogram>
 
@@ -23056,6 +23055,14 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   </summary>
 </histogram>
 
+<histogram name="NewTabPage.LoadTime">
+  <owner>fserb@chromium.org</owner>
+  <summary>
+    Histogram of the time, in milliseconds, it took for the NTP to load all its
+    tiles since navigation start.
+  </summary>
+</histogram>
+

[beaudoin, 2015/03/16 19:39:36]

Could you look for "Recorded before changing focus away from the NTP" in that
file and rephrase them to indicate the fact that you're sending them too if the
page sends new suggestions before navigation occurs. 

[fserb, 2015/03/16 19:47:38]

Done.

 <histogram name="NewTabPage.MobilePromo" enum="NewTabPageMobilePromo">
   <obsolete>
     Deprecated on M33 with the change to native NTP.