PlzNavigate: Add metrics to understand bf navigations PLT regression

tools/metrics/histograms/enums.xml

Index: tools/metrics/histograms/enums.xml
diff --git a/tools/metrics/histograms/enums.xml b/tools/metrics/histograms/enums.xml
index 0c4a5dccd1a8277027244eef76d05bca683b9b1e..fbb3d0e7fc5fb52f2a31753b3b3fbc09e098e35a 100644
--- a/tools/metrics/histograms/enums.xml
+++ b/tools/metrics/histograms/enums.xml
@@ -25193,6 +25193,14 @@ from previous Chrome versions.
   <int value="3" label="Behind a Non-Symmetric NAT."/>
 </enum>
 
+<enum name="NavigationCacheEnum" type="int">
+  <int value="0" label="Validate cache"/>
+  <int value="1" label="Bypass cache"/>
+  <int value="2" label="Skip cache validation"/>
+  <int value="3" label="Only from cache"/>
+  <int value="4" label="Disable cache"/>
+</enum>
+
 <enum name="NavigationDirection" type="int">
   <obsolete>
     Deprecated as of Chrome 59 in favour of OverscrollNavigationType.
@@ -25210,6 +25218,11 @@ from previous Chrome versions.
   <int value="3" label="Navigation not intercepted"/>
 </enum>
 
+<enum name="NavigationIsSameProcess" type="int">
+  <int value="0" label="Cross process navigation"/>
+  <int value="1" label="Same process navigation"/>
+</enum>
+
 <enum name="NavigationScheme" type="int">
   <int value="0" label="(Unknown)"/>
   <int value="1" label="http"/>
@@ -25224,6 +25237,11 @@ from previous Chrome versions.
   <int value="10" label="filesystem"/>
 </enum>
 
+<enum name="NavigationWasServedFromCache" type="int">
+  <int value="0" label="Navigation wasn't served from cache"/>
+  <int value="1" label="Navigation was served from cache"/>
+</enum>
+
 <enum name="NavigatorVibrationType" type="int">
   <int value="0" label="Main frame vibrate, no user gesture"/>
   <int value="1" label="Main frame vibrate, with user gesture"/>