base: Add ScopedJavaLocalFrame class.

base/android/scoped_java_ref.h

Index: base/android/scoped_java_ref.h
diff --git a/base/android/scoped_java_ref.h b/base/android/scoped_java_ref.h
index a5d71e2d23b9b8d7ad0447ed7c9c2b54e905c83b..08893006c1569e0f89d03ab5f631358986d92ad7 100644
--- a/base/android/scoped_java_ref.h
+++ b/base/android/scoped_java_ref.h
@@ -148,6 +148,23 @@ class ScopedJavaLocalRef : public JavaRef<T> {
   JNIEnv* env_;
 };
 
+// Creates a new local reference frame, in which at least a given number of
+// local references can be created. Note that local references already created
+// in previous local frames are still valid in the current local frame.
+class BASE_EXPORT ScopedJavaLocalFrame {

[bulach, 2014/04/07 15:51:29]

nit: may I ask to move this one either as the first one on the top of this file?
:) reason being that LocalRef and GlobalRef are somewhat related...

[reveman, 2014/04/07 17:38:29]

Done.

+ public:
+  explicit ScopedJavaLocalFrame(JNIEnv* env);
+  ScopedJavaLocalFrame(JNIEnv* env, int capacity);
+  ~ScopedJavaLocalFrame();
+
+ private:
+  // This class is only good for use on the thread it was created on so
+  // it's safe to cache the non-threadsafe JNIEnv* inside this object.
+  JNIEnv* env_;
+
+  DISALLOW_COPY_AND_ASSIGN(ScopedJavaLocalFrame);
+};
+
 // Holds a global reference to a Java object. The global reference is scoped
 // to the lifetime of this object. This class does not hold onto any JNIEnv*
 // passed to it, hence it is safe to use across threads (within the constraints