Measure inappropriate_fallback alerts from Google.

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 a7019e3dca6785a46bd0e7747a3d286040faaf76..495a44c4f10f1a1989078dcc435d3fce186ed596 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -19457,6 +19457,17 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   </summary>
 </histogram>
 
+<histogram name="Net.GoogleConnectionInappropriateFallback"
+    enum="BooleanInappropriateFallback">
+  <owner>davidben@chromium.org</owner>
+  <summary>
+    Records a sample for each HTTPS request to a Google server that either
+    succeeded or received an inappropriate_fallback alert. This is used to
+    estimate how frequently the fallback is used to recover from a spurious
+    network failure.
+  </summary>
+</histogram>
+
 <histogram name="Net.GoogleConnectionUsedSSLVersionFallback"
     enum="FallbackSSLVersion">
   <obsolete>
@@ -19477,8 +19488,8 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   <summary>
     For each successful HTTPS request to a Google server, whether it used the
     SSL version fallback. The value indicates the SSL version the request fell
-    back on. Since Google servers support TLS 1.2, any fallback is an indication
-    of network middleware problems.
+    back on. Since Google servers support TLS 1.2 and FALLBACK_SCSV, any
+    fallback is an indication of a broken local SSL MITM proxy.
   </summary>
 </histogram>
 
@@ -48265,6 +48276,11 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   <int value="1" label="Ignored"/>
 </enum>
 
+<enum name="BooleanInappropriateFallback" type="int">
+  <int value="0" label="Handshake successful"/>
+  <int value="1" label="inappropriate_fallback alert"/>

[Ilya Sherman, 2015/05/18 18:55:34]

nit: Why not "Inappropriate fallback alert"?  (Which I'd personally further
tweak to "Inappropriate fallback used", but that's mostly a personal
preference.)

[davidben, 2015/05/18 19:09:09]

Alerts are a type of error in the TLS protocol and inappropriate_fallback is the
name of the alert. The server is sending us the inappropriate_fallback alert.

+</enum>
+
 <enum name="BooleanIsMobileOptimized" type="int">
   <int value="0" label="Not mobile optimized web page"/>
   <int value="1" label="Mobile optimized web page"/>