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..0b8acba2b44295f98e5f3fdfd4c098f6d13b0b64 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
     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="NewRenderer_BeforeUnloadDiscounted"
+      label="Navigation spawned a new renderer process. Time spent in
+             beforeunload subtracted."/>
+  <suffix name="NewRenderer_Restored_BeforeUnloadDiscounted"
+      label="Navigation spawned a new renderer process and is restored from a
+             previous session (whether from a crash or a continued session).
+             Time spent in beforeunload subtracted."/>
+  <suffix name="OldRenderer_BeforeUnloadDiscounted"

[clamy, 2014/10/13 15:28:33]

I would rather use the name ExistingRenderer instead of OldRenderer.

[carlosk, 2014/10/13 18:01:46]

Done.

+      label="Navigation reused an existing renderer process. 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>