Relanding: Break peerconnection_jni.cc into multiple files, in "pc" directory.

webrtc/sdk/android/src/jni/jni_helpers.h

Index: webrtc/sdk/android/src/jni/jni_helpers.h
diff --git a/webrtc/sdk/android/src/jni/jni_helpers.h b/webrtc/sdk/android/src/jni/jni_helpers.h
index 19b7741fb58633f1d0d288fceb024b71c7a661ad..e4c43a25bf2396ead2de0b449082df4f253b4759 100644
--- a/webrtc/sdk/android/src/jni/jni_helpers.h
+++ b/webrtc/sdk/android/src/jni/jni_helpers.h
@@ -34,6 +34,23 @@
 #define CHECK_RELEASE(ptr) \
   RTC_CHECK_EQ(0, (ptr)->Release()) << "Unexpected refcount."
 
+// Convenience macro defining JNI-accessible methods in the org.webrtc package.
+// Eliminates unnecessary boilerplate and line-wraps, reducing visual clutter.
+//
+// TODO(deadbeef): Rename this macro to something like
+// "JNI_FUNCTION_DECLARATION", and use variable length arguments, such that you
+// can write:
+//
+// JNI_FUNCTION_DECLARATION(void, nativeFoo, Type arg1, Type arg2) { ...
+//
+// Instead of:
+//
+// JNI_FUNCTION_DECLARATION(void, nativeFoo)(Type arg1, Type arg2) { ...
+//
+// The latter gets handled poorly by autoformatting tools.
+#define JOW(rettype, name) \
+  extern "C" JNIEXPORT rettype JNICALL Java_org_webrtc_##name
+
 namespace webrtc_jni {
 
 jint InitGlobalJniVariables(JavaVM *jvm);
@@ -97,6 +114,12 @@ std::string JavaToStdString(JNIEnv* jni, const jstring& j_string);
 jobject JavaEnumFromIndex(JNIEnv* jni, jclass state_class,
                           const std::string& state_class_name, int index);
 
+// Return the (singleton) Java Enum object corresponding to |index|;
+// |state_class_fragment| is something like "MediaSource$State".
+jobject JavaEnumFromIndexAndClassName(JNIEnv* jni,
+                                      const std::string& state_class_fragment,
+                                      int index);
+
 // Returns the name of a Java enum.
 std::string GetJavaEnumName(JNIEnv* jni,
                             const std::string& className,