Refactor the BluetoothDispatcherHost to store requestDevice sessions

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 554a46cdec308c9a7986652b310f2c127c4091fd..13707dc781af123cfe8d19b08f19380b30adf8be 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -50917,6 +50917,7 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <int value="90" label="BDH_INVALID_WRITE_VALUE_LENGTH"/>
   <int value="91" label="WC_MEMORY_CACHE_RESOURCE_BAD_SECURITY_INFO"/>
   <int value="92" label="WC_RENDERER_DID_NAVIGATE_BAD_SECURITY_INFO"/>
+  <int value="93" label="BDH_DUPLICATE_REQUEST_DEVICE_ID"/>

[Alexei Svitkine (slow), 2015/07/15 13:22:57]

Given that this list has grown recently, it would be better to use a sparse
histogram to log the values.

Would you mind changing:

 UMA_HISTOGRAM_ENUMERATION("Stability.BadMessageTerminated.Content", reason,
                            BAD_MESSAGE_MAX);

to:

UMA_HISTOGRAM_SPARSE_SLOWLY("Stability.BadMessageTerminated.Content", reason);

 </enum>
 
 <enum name="BadMessageReasonExtensions" type="int">