Move CHA state keeping from Isolate to Thread.

runtime/vm/thread.h

Index: runtime/vm/thread.h
===================================================================
--- runtime/vm/thread.h	(revision 44544)
+++ runtime/vm/thread.h	(working copy)
@@ -10,7 +10,7 @@
 namespace dart {
 
 // A VM thread; may be executing Dart code or performing helper tasks like
-// garbage collection.
+// garbage collection or compilation.
 class Thread {
  public:
   static Thread* Current() {
@@ -17,7 +17,7 @@
     // For now, there is still just one thread per isolate, and the Thread
     // class just aliases the Isolate*. Once all interfaces and uses have been
     // updated to distinguish between isolates and threads, Thread will get its
-    // own thread-local storage key.
+    // own thread-local storage key and fields.
     return reinterpret_cast<Thread*>(Isolate::Current());
   }
   // TODO(koda): Remove after pivoting to Thread* in native/runtime entries.
@@ -32,8 +32,9 @@
   }
 
   // The isolate that this thread is operating on.
-  Isolate* isolate() {
-    return reinterpret_cast<Isolate*>(this);
+  Isolate* isolate() { return reinterpret_cast<Isolate*>(this); }
+  const Isolate* isolate() const {
+    return reinterpret_cast<const Isolate*>(this);
   }
 
   // The log for this thread.
@@ -41,6 +42,10 @@
     return reinterpret_cast<Isolate*>(this)->Log();
   }
 
+  // The (topmost) CHA for the compilation in this thread.
+  CHA* cha() const { return isolate()->cha(); }
+  void set_cha(CHA* value) { isolate()->set_cha(value); }
+
  private:
   DISALLOW_COPY_AND_ASSIGN(Thread);
 };