Use Android callback API to obtain cellular signal strength

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 544b09fd904c4ae81a8a3d3588ebdf3143ba5bd8..704594be919e087f862ec45fb3e483a8e8bb8a2f 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -4123,12 +4123,12 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <owner>szhangcs@google.com</owner>
   <summary>
     Autofill form events for credit card forms. These are recorded when the user
-    interacts with a form requesting a credit card, a dropdown of suggestions
-    is shown and at least one of the suggestions has a bank name. Form events
-    are logged at most once per page load.
+    interacts with a form requesting a credit card, a dropdown of suggestions is
+    shown and at least one of the suggestions has a bank name. Form events are
+    logged at most once per page load.
   </summary>
   <details>
-    These metrics are used to measure the impact of the bank name experiment. 
+    These metrics are used to measure the impact of the bank name experiment.
     They are used to calculate the CTR of the autofill UI with bank names
     available. Not all credit cards will have bank names even if we launch the
     experiment. With these metrics we can run the experiment on 2 groups. For
@@ -45969,7 +45969,33 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="NQE.CellularSignalStrength.LevelAvailable"
+    enum="BooleanAvailable">
+  <owner>tbansal@chromium.org</owner>
+  <owner>bengr@chromium.org</owner>
+  <summary>
+    Whether the signal strength for the cellular network was available or not.
+    Recorded right before a connection change event. Recorded only on cellular
+    connections on Android platform.
+  </summary>
+</histogram>
+
+<histogram name="NQE.CellularSignalStrength.LevelDifference"
+    units="Signal Strength Level">
+  <owner>tbansal@chromium.org</owner>
+  <owner>bengr@chromium.org</owner>
+  <summary>
+    Difference between the minimum and the maximum received signal strength
+    since the last connection change event. Recorded only on cellular
+    connections on Android platform when the cellular signal strength was
+    available. Recorded right before a connection change event.
+  </summary>
+</histogram>
+
 <histogram name="NQE.CellularSignalStrengthAvailable" enum="BooleanAvailable">
+  <obsolete>
+    Replaced by NQE.CellularSignalStrength.LevelAvailable in June 2017.
+  </obsolete>
   <owner>tbansal@chromium.org</owner>
   <owner>bengr@chromium.org</owner>
   <summary>
@@ -45980,6 +46006,9 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
 </histogram>
 
 <histogram name="NQE.CellularSignalStrengthDifference" units="dBm">
+  <obsolete>
+    Replaced by NQE.CellularSignalStrength.LevelDifference in June 2017.
+  </obsolete>
   <owner>tbansal@chromium.org</owner>
   <owner>bengr@chromium.org</owner>
   <summary>