Optimize memory-footprint for RemoteLookupTrackerClient

Observations:
- In case of !requiresPosition we don't need to track position
- Also, in the latter case we don't need scopeKind (implicit contract)
- There were a lot of LookupInfo instances having two references
(fileName/scopeFqName) pointing to the same strings.
Looks like in common case (reasonable amount of files/fqnames) it's more
sensible to group lookups in the two-level-tree (implemented with nested maps)

It's expected to decrease memory consumption up to 15M in case of compiling
`idea` module in Kotlin project

compiler/daemon/src/org/jetbrains/kotlin/daemon/RemoteLookupTrackerClient.kt

@@ -17,6 +17,7 @@
 package org.jetbrains.kotlin.daemon
 
 import com.intellij.util.containers.StringInterner
+import gnu.trove.THashMap
 import gnu.trove.THashSet
 import org.jetbrains.kotlin.daemon.common.CompilerCallbackServicesFacade
 import org.jetbrains.kotlin.daemon.common.DummyProfiler
@@ -27,10 +28,15 @@ import org.jetbrains.kotlin.incremental.components.Position
 import org.jetbrains.kotlin.incremental.components.ScopeKind
 
 
-class RemoteLookupTrackerClient(val facade: CompilerCallbackServicesFacade, eventManager: EventManager, val profiler: Profiler = DummyProfiler()) : LookupTracker {
+class RemoteLookupTrackerClient(
+    val facade: CompilerCallbackServicesFacade,
+    eventManager: EventManager,
+    val profiler: Profiler = DummyProfiler()
+) : LookupTracker {
     private val isDoNothing = profiler.withMeasure(this) { facade.lookupTracker_isDoNothing() }
 
-    private val lookups = THashSet<LookupInfo>()
+    // Map: FileName -> (ScopeFqName -> Set<Name[String] | LookupInfo>)
+    private val lookups = THashMap<String, MutableMap<String, MutableSet<Any>>>()
     private val interner = StringInterner()
 
     override val requiresPosition: Boolean = profiler.withMeasure(this) { facade.lookupTracker_requiresPosition() }
@@ -38,11 +44,16 @@ class RemoteLookupTrackerClient(val facade: CompilerCallbackServicesFacade, even
     override fun record(filePath: String, position: Position, scopeFqName: String, scopeKind: ScopeKind, name: String) {
         if (isDoNothing) return
 
-        val internedFilePath = interner.intern(filePath)
-        val internedScopeFqName = interner.intern(scopeFqName)
+        val internedSymbolFqName = interner.intern(scopeFqName)
         val internedName = interner.intern(name)
 
-        lookups.add(LookupInfo(internedFilePath, position, internedScopeFqName, scopeKind, internedName))
+        val objectToPut: Any =
+            if (requiresPosition)
+                LookupInfo(filePath, position, scopeFqName, scopeKind, name)
+            else
+                internedName
+
+        lookups.getOrPut(filePath, ::THashMap).getOrPut(internedSymbolFqName, ::THashSet).add(objectToPut)
     }
 
     init {
@@ -50,11 +61,24 @@ class RemoteLookupTrackerClient(val facade: CompilerCallbackServicesFacade, even
     }
 
     private fun flush() {
-        if (isDoNothing || lookups.isEmpty()) return
+        if (isDoNothing || lookups.isEmpty) return
 
         profiler.withMeasure(this) {
-            // Converting to list is intentional because THashSet may lead to serialization-related problems
-            facade.lookupTracker_record(lookups.toList())
+            facade.lookupTracker_record(
+                lookups.flatMap { (filePath, lookupsByFile) ->
+                    lookupsByFile.flatMap { (scopeFqName, lookupsByScopeFqName) ->
+                        lookupsByScopeFqName.map { lookupInfoOrString ->
+                            if (requiresPosition)
+                                lookupInfoOrString as LookupInfo
+                            else
+                                LookupInfo(
+                                    filePath, Position.NO_POSITION, scopeFqName, ScopeKind.CLASSIFIER,
+                                    lookupInfoOrString as String
+                                )
+                        }
+                    }
+                }
+            )
         }
 
         lookups.clear()