Remove register counts from VirtualFrame, use register indices instead.

src/virtual-frame-ia32.h

Index: src/virtual-frame-ia32.h
===================================================================
--- src/virtual-frame-ia32.h	(revision 1604)
+++ src/virtual-frame-ia32.h	(working copy)
@@ -76,10 +76,18 @@
     return elements_.length() - expression_base_index();
   }
 
-  int register_count(Register reg) {
-    return frame_registers_.count(reg);
+  int register_index(Register reg) {
+    return register_locations_[reg.code()];
   }
 
+  bool is_used(int reg_code) {
+    return register_locations_[reg_code] != kIllegalIndex;
+  }
+
+  bool is_used(Register reg) {
+    return is_used(reg.code());
+  }
+
   // Add extra in-memory elements to the top of the frame to match an actual
   // frame (eg, the frame after an exception handler is pushed).  No code is
   // emitted.
@@ -333,10 +341,6 @@
   // (the ebp register).
   int frame_pointer_;
 
-  // The frame has an embedded register file that it uses to track registers
-  // used in the frame.
-  RegisterFile frame_registers_;
-
   // The index of the register frame element using each register, or
   // kIllegalIndex if a register is not on the frame.
   int register_locations_[kNumRegisters];