Oilpan: Split Heap.h into two files

To reduce a mess of Heap.h, this CL splits Heap.h into Heap.h and HeapPage.h.

This CL just moves code around without any behavioral change.

BUG=437144

Review URL: https://codereview.chromium.org/1314793002

git-svn-id: svn://svn.chromium.org/blink/trunk@201109 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/Source/platform/heap/BUILD.gn

@@ -20,6 +20,8 @@ source_set("heap") {
     "Heap.h",
     "HeapAllocator.cpp",
     "HeapAllocator.h",
+    "HeapPage.cpp",
+    "HeapPage.h",
     "InlinedGlobalMarkingVisitor.h",
     "MarkingVisitor.h",
     "MarkingVisitorImpl.h",

third_party/WebKit/Source/platform/heap/blink_heap.gypi

@@ -43,6 +43,8 @@
       'Heap.h',
       'HeapAllocator.cpp',
       'HeapAllocator.h',
+      'HeapPage.cpp',
+      'HeapPage.h',
       'InlinedGlobalMarkingVisitor.h',
       'MarkingVisitor.h',
       'MarkingVisitorImpl.h',