VM: Use PC offset instead of absolute PC in exception handler info.

runtime/vm/raw_object.h

Index: runtime/vm/raw_object.h
===================================================================
--- runtime/vm/raw_object.h	(revision 43106)
+++ runtime/vm/raw_object.h	(working copy)
@@ -1200,7 +1200,7 @@
   // The index into the ExceptionHandlers table corresponds to
   // the try_index of the handler.
   struct HandlerInfo {
-    intptr_t handler_pc;       // PC value of handler.
+    uint32_t handler_pc_offset;  // PC offset value of handler.
     int16_t outer_try_index;   // Try block index of enclosing try block.
     int8_t needs_stacktrace;   // True if a stacktrace is needed.
     int8_t has_catch_all;      // Catches all exceptions.