Report Android Build.MODEL in SystemProfileProto hardware_class.

components/metrics/proto/system_profile.proto

Index: components/metrics/proto/system_profile.proto
diff --git a/components/metrics/proto/system_profile.proto b/components/metrics/proto/system_profile.proto
index ca277cb0eefc13418d7bafc52a674c7e2d11214f..68df86901b159a04df93c133bb4889f22dad5b21 100644
--- a/components/metrics/proto/system_profile.proto
+++ b/components/metrics/proto/system_profile.proto
@@ -112,10 +112,14 @@ message SystemProfileProto {
     // (Logged only on Windows.)
     optional int64 dll_base = 3;
 
-    // The Chrome OS device hardware class ID is a unique string associated with
-    // each Chrome OS device product revision generally assigned at hardware
-    // qualification time.  The hardware class effectively identifies the
-    // configured system components such as CPU, WiFi adapter, etc.
+    // The hardware_class describes the current machine model, e.g. "MacPro1,1"

[Alexei Svitkine (slow), 2015/07/21 16:52:11]

Can you also send a CL to update this comment in the internal copy of this
proto? Thanks!

+    // on Mac, or "Nexus 5" on Android. Only implemented on OS X, Android, and
+    // Chrome OS.
+    //
+    // For Chrome OS, the device hardware class ID is a unique string associated
+    // with each Chrome OS device product revision generally assigned at
+    // hardware qualification time. The hardware class effectively identifies
+    // the configured system components such as CPU, WiFi adapter, etc.
     //
     // An example of such a hardware class is "IEC MARIO PONY 6101".  An
     // internal database associates this hardware class with the qualified