Use one offsets table per generated irregexp matching function.

runtime/vm/regexp.h

Index: runtime/vm/regexp.h
diff --git a/runtime/vm/regexp.h b/runtime/vm/regexp.h
index 2675aaaf5a51ffe9ebd0fb29d4510ae1095abcc9..4b8d19c0eb12df0178d5c2844beb2a28bf228186 100644
--- a/runtime/vm/regexp.h
+++ b/runtime/vm/regexp.h
@@ -1372,26 +1372,21 @@ class RegExpEngine: public AllStatic {
  public:
   struct CompilationResult {
     explicit CompilationResult(const char* error_message)
-        : macro_assembler(NULL),
-          graph_entry(NULL),
+        : graph_entry(NULL),
           num_blocks(-1),
           num_stack_locals(-1),
           error_message(error_message) {}
-    CompilationResult(IRRegExpMacroAssembler* macro_assembler,
-                      GraphEntryInstr* graph_entry,
+    CompilationResult(GraphEntryInstr* graph_entry,
                       intptr_t num_blocks,
                       intptr_t num_stack_locals)
-      : macro_assembler(macro_assembler),
-        graph_entry(graph_entry),
+      : graph_entry(graph_entry),
         num_blocks(num_blocks),
         num_stack_locals(num_stack_locals),
         error_message(NULL) {}
 
-    IRRegExpMacroAssembler* macro_assembler;
     GraphEntryInstr* graph_entry;
     const intptr_t num_blocks;
     const intptr_t num_stack_locals;
-
     const char* error_message;
   };