Add usage display support for Extension IME.

chrome/browser/chromeos/input_method/input_method_engine.h

Index: chrome/browser/chromeos/input_method/input_method_engine.h
diff --git a/chrome/browser/chromeos/input_method/input_method_engine.h b/chrome/browser/chromeos/input_method/input_method_engine.h
index a1887804e959875c5f40350feb60cf14ca6e9ca5..96f7cb8dd3a2615a4f123ad623ebc1ce6b3bdc12 100644
--- a/chrome/browser/chromeos/input_method/input_method_engine.h
+++ b/chrome/browser/chromeos/input_method/input_method_engine.h
@@ -78,6 +78,11 @@ class InputMethodEngine {
     std::string type;
   };
 
+  struct UsageEntry {
+    std::string title;
+    std::string body;
+  };
+
   struct Candidate {
     Candidate();
     virtual ~Candidate();
@@ -86,6 +91,7 @@ class InputMethodEngine {
     int id;
     std::string label;
     std::string annotation;
+    UsageEntry usage;
     std::vector<Candidate> candidates;
   };