Changes PlzNavitate histograms to try and simplify their multi-modal characteristic.

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 adc182ab5fc438020e7300ca0c02359542a75e0a..866e8462f424e1275db7868d8750191de31cf8cd 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -13878,7 +13878,7 @@ Therefore, the affected-histogram name has to have at least one dot in it.
 <histogram name="Navigation.TimeToCommit" units="milliseconds">
   <owner>carlosk@chromium.org</owner>
   <summary>
-    Time between the start of a navigation request in the browser and its
+    Time between the start of a browser started navigation request in and its

[Ilya Sherman, 2014/10/13 22:05:55]

Optional nit: Perhaps "browser-started" rather than "browser started"?  (Ditto
below)

[carlosk, 2014/10/14 09:03:27]

Done.

     commit.
   </summary>
 </histogram>
@@ -13886,7 +13886,7 @@ Therefore, the affected-histogram name has to have at least one dot in it.
 <histogram name="Navigation.TimeToURLJobStart" units="milliseconds">
   <owner>carlosk@chromium.org</owner>
   <summary>
-    Time between the start of a navigation request in the browser and the
+    Time between the start of a browser started navigation request and the
     reception of a corresponding ResourceRequest in the network stack.
   </summary>
 </histogram>
@@ -54539,6 +54539,21 @@ To add a new entry, add it with any value and run test to compute valid value.
   <affected-histogram name="Media.VideoCaptureManager"/>
 </histogram_suffixes>
 
+<histogram_suffixes name="NavigationCharacteristic">
+  <suffix name="ExistingRenderer_BeforeUnloadDiscounted"
+      label="Navigation reused an existing renderer process. Time spent in
+             beforeunload subtracted."/>
+  <suffix name="NewRenderer_BeforeUnloadDiscounted"
+      label="Navigation spawned a new renderer process. Time spent in
+             beforeunload subtracted."/>
+  <suffix name="SessionRestored"
+      label="Navigation caused by restoring a tab from a previous session
+             (whether from a crash or a continued session) either spawning or
+             reusing a renderer. Time spent in beforeunload subtracted."/>
+  <affected-histogram name="Navigation.TimeToCommit"/>
+  <affected-histogram name="Navigation.TimeToURLJobStart"/>
+</histogram_suffixes>
+
 <histogram_suffixes name="Net.QuicClientHelloRejectReasons.QuicIsSecureOrNot"
     separator=".">
   <owner>rtenneti@chromium.org</owner>