Move a bunch of GC related files to heap/ subdirectory

BUILD.gn

Index: BUILD.gn
diff --git a/BUILD.gn b/BUILD.gn
index 139a895acdb8c7815b64bb3b1c0df7db789c0451..b1be5760b345fc5f2250a4000b53c4942c9c9c02 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -632,8 +632,6 @@ source_set("v8_base") {
     "src/full-codegen.h",
     "src/func-name-inferrer.cc",
     "src/func-name-inferrer.h",
-    "src/gc-tracer.cc",
-    "src/gc-tracer.h",
     "src/gdb-jit.cc",
     "src/gdb-jit.h",
     "src/global-handles.cc",
@@ -643,14 +641,26 @@ source_set("v8_base") {
     "src/handles.cc",
     "src/handles.h",
     "src/hashmap.h",
-    "src/heap-inl.h",
     "src/heap-profiler.cc",
     "src/heap-profiler.h",
     "src/heap-snapshot-generator-inl.h",
     "src/heap-snapshot-generator.cc",
     "src/heap-snapshot-generator.h",
-    "src/heap.cc",
-    "src/heap.h",
+    "src/heap/gc-tracer.cc",
+    "src/heap/gc-tracer.h",
+    "src/heap/heap-inl.h",
+    "src/heap/heap.cc",
+    "src/heap/heap.h",
+    "src/heap/incremental-marking.cc",
+    "src/heap/incremental-marking.h",
+    "src/heap/mark-compact-inl.h",
+    "src/heap/mark-compact.cc",
+    "src/heap/mark-compact.h",
+    "src/heap/spaces-inl.h",
+    "src/heap/spaces.cc",
+    "src/heap/spaces.h",
+    "src/heap/sweeper-thread.h",
+    "src/heap/sweeper-thread.cc",
     "src/hydrogen-alias-analysis.h",
     "src/hydrogen-bce.cc",
     "src/hydrogen-bce.h",
@@ -710,8 +720,6 @@ source_set("v8_base") {
     "src/ic-inl.h",
     "src/ic.cc",
     "src/ic.h",
-    "src/incremental-marking.cc",
-    "src/incremental-marking.h",
     "src/interface.cc",
     "src/interface.h",
     "src/interpreter-irregexp.cc",
@@ -742,8 +750,6 @@ source_set("v8_base") {
     "src/lookup.cc",
     "src/lookup.h",
     "src/macro-assembler.h",
-    "src/mark-compact.cc",
-    "src/mark-compact.h",
     "src/messages.cc",
     "src/messages.h",
     "src/msan.h",
@@ -811,9 +817,6 @@ source_set("v8_base") {
     "src/snapshot-source-sink.cc",
     "src/snapshot-source-sink.h",
     "src/snapshot.h",
-    "src/spaces-inl.h",
-    "src/spaces.cc",
-    "src/spaces.h",
     "src/store-buffer-inl.h",
     "src/store-buffer.cc",
     "src/store-buffer.h",
@@ -825,8 +828,6 @@ source_set("v8_base") {
     "src/strtod.h",
     "src/stub-cache.cc",
     "src/stub-cache.h",
-    "src/sweeper-thread.h",
-    "src/sweeper-thread.cc",
     "src/token.cc",
     "src/token.h",
     "src/transitions-inl.h",