Don't use Singleton to cache JNI method IDs in Java Bridge

base/android/jni_android.h

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef BASE_ANDROID_JNI_ANDROID_H_
 #define BASE_ANDROID_JNI_ANDROID_H_
 
 #include <jni.h>
 #include <sys/types.h>
 
@@ skipping 12 matching lines @@
 
 // Initializes the global application context object. The |context| should be
 // the global reference of application context object.  It is not necessarily
 // called after InitVM().
 // TODO: We might combine InitVM() and InitApplicationContext() into one method.
 void InitApplicationContext(jobject context);
 
 // Returns the application context assigned by InitApplicationContext().
 jobject GetApplicationContext();
 
-// Wraps a method ID.
-class MethodID {
- public:
-  jmethodID id() { return id_; }
- protected:
-  // Gets the method ID from the class name. Clears the pending Java exception
-  // and returns NULL if the method is not found. Note that GetMethodID() below
-  // avoids a class lookup, so should be used in preference when possible.
-  MethodID(JNIEnv* env, const char* class_name, const char* method,
-           const char* jni_signature);
- private:
-  jmethodID id_;
-};
+// Gets the method ID from the class name. Clears the pending Java exception
+// and returns NULL if the method is not found. Caches results. Note that
+// GetMethodID() below avoids a class lookup, but does not cache results.
+// Strings passed to this function are held in the cache and MUST remain valid
+// beyond the duration of all future calls to this function, across all
+// threads. In practice, this means that the function should only be used with
+// string constants.
+jmethodID GetMethodIDFromClassName(JNIEnv* env,
+                                   const char* class_name,
+                                   const char* method,
+                                   const char* jni_signature);
 
 // Get the method ID for a method. Will clear the pending Java
 // exception and return 0 if the method is not found.
 jmethodID GetMethodID(JNIEnv* env,
                       jclass clazz,
                       const char* const method,
                       const char* const jni_signature);
 
 // Get the method ID for a class static method. Will clear the pending Java
 // exception and return 0 if the method is not found.
@@ skipping 10 matching lines @@
                     const char* jni_signature);
 
 // Returns true if an exception is pending in the provided JNIEnv*. If an
 // exception is pending, this function prints and then clears it.
 bool CheckException(JNIEnv* env);
 
 }  // namespace android
 }  // namespace base
 
 #endif  // BASE_ANDROID_JNI_ANDROID_H_