Allow to embed source files into JS source maps

js/js.ast/src/org/jetbrains/kotlin/js/backend/ast/JsLocation.kt

@@ -16,8 +16,31 @@
 
 package org.jetbrains.kotlin.js.backend.ast
 
+import java.io.Reader
+
 data class JsLocation(
-        val file: String,
-        val startLine: Int,
-        val startChar: Int
-)
+        override val file: String,
+        override val startLine: Int,
+        override val startChar: Int
+) : JsLocationWithSource {
+    override val identityObject: Any? = null
+    override val sourceProvider: () -> Reader? = { null }
+
+    override fun asSimpleLocation(): JsLocation = this
+}
+
+interface JsLocationWithSource {
+    val file: String
+    val startLine: Int
+    val startChar: Int
+    val identityObject: Any?
+    val sourceProvider: () -> Reader?
+
+    fun asSimpleLocation(): JsLocation
+}
+
+class JsLocationWithEmbeddedSource(
+        private val location: JsLocation,
+        override val identityObject: Any?,
+        override val sourceProvider: () -> Reader?
+) : JsLocationWithSource by location