Refactor the Heap into ThreadHeap to prepare for per thread heaps

third_party/WebKit/Source/platform/exported/Platform.cpp

Index: third_party/WebKit/Source/platform/exported/Platform.cpp
diff --git a/third_party/WebKit/Source/platform/exported/Platform.cpp b/third_party/WebKit/Source/platform/exported/Platform.cpp
index d78268f61838747b130645940de022d31a15a752..6fedfe75108e78b638933ead3591c881cadcca86 100644
--- a/third_party/WebKit/Source/platform/exported/Platform.cpp
+++ b/third_party/WebKit/Source/platform/exported/Platform.cpp
@@ -91,7 +91,7 @@ void Platform::initialize(Platform* platform)
     WTF::initialize();
     WTF::initializeMainThread(callOnMainThreadFunction);
 
-    Heap::init();
+    ProcessHeap::init();
 
     ThreadState::attachMainThread();
 
@@ -123,7 +123,7 @@ void Platform::shutdown()
     // so that the main thread won't get involved in a GC during the shutdown.
     ThreadState::detachMainThread();
 
-    Heap::shutdown();
+    ProcessHeap::shutdown();
 
     WTF::shutdown();
     WTF::Partitions::shutdown();