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 01e6809e03ca3e89f81aeb43d388576ee5f0ddf2..9cc148acc1eeb8f51121fc820eaefe36e17afe0e 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -13757,7 +13757,25 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   </summary>
 </histogram>
 
-<histogram name="Navigation.TimeToCommit" units="milliseconds">

[Ilya Sherman, 2014/10/07 20:23:45]

Please mark the obsolete histograms as <obsolete> rather than deleting their
descriptions.

[carlosk, 2014/10/09 16:53:45]

Acknowledged how this is supposed to be handled and I'll in fact revert them to
the old names. For now I'd like to have them just in case they helps us better
understand how these timings actually work but they might be made obsolete in
the future.

+<histogram name="Navigation.TimeToCommitNewRenderer" units="milliseconds">
+  <owner>carlosk@chromium.org</owner>
+  <summary>
+    Time between the start of a navigation request in the browser and its commit
+    if it required the spawning of a new renderer process and discounting any

[Ilya Sherman, 2014/10/07 20:23:45]

nit: "new renderer process and discounting" -> "new renderer process. Discounts"
 (applies throughout)

[carlosk, 2014/10/09 16:53:45]

Done.

+    time spent with the beforeunload event.

[Ilya Sherman, 2014/10/07 20:23:45]

nit: "spent with" -> "spent in" (applies throughout)

[carlosk, 2014/10/09 16:53:45]

Done.

+  </summary>
+</histogram>
+
+<histogram name="Navigation.TimeToCommitOldRenderer" units="milliseconds">

[Ilya Sherman, 2014/10/07 20:23:45]

Optional: You might want to use a <histogram_suffixes> element to reduce the
amount of repetition in these histogram descriptions.

[carlosk, 2014/10/09 16:53:45]

This is nice and fits like a glove, especially now that I realized I'd better
keep the old behavior and names (not add the "Raw" suffix) to keep the existing
metrics as they are right now.

+  <owner>carlosk@chromium.org</owner>
+  <summary>
+    Time between the start of a navigation request in the browser and its commit
+    if it reused an existing renderer process and discounting any time spent
+    with the beforeunload event.
+  </summary>
+</histogram>
+
+<histogram name="Navigation.TimeToCommitRaw" units="milliseconds">
   <owner>carlosk@chromium.org</owner>
   <summary>
     Time between the start of a navigation request in the browser and its
@@ -13765,7 +13783,27 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   </summary>
 </histogram>
 
-<histogram name="Navigation.TimeToURLJobStart" units="milliseconds">
+<histogram name="Navigation.TimeToURLJobNewRenderer" units="milliseconds">
+  <owner>carlosk@chromium.org</owner>
+  <summary>
+    Time between the start of a navigation request in the browser and the
+    reception of a corresponding ResourceRequest in the network stack, if it
+    required the spawning of a new renderer process and discounting any time
+    spent with the beforeunload event.
+  </summary>
+</histogram>
+
+<histogram name="Navigation.TimeToURLJobOldRenderer" units="milliseconds">
+  <owner>carlosk@chromium.org</owner>
+  <summary>
+    Time between the start of a navigation request in the browser and the
+    reception of a corresponding ResourceRequest in the network stack, if it
+    reused an existing renderer process and discounting any time spent with the
+    beforeunload event.
+  </summary>
+</histogram>
+
+<histogram name="Navigation.TimeToURLJobStartRaw" units="milliseconds">
   <owner>carlosk@chromium.org</owner>
   <summary>
     Time between the start of a navigation request in the browser and the