Rename InstructionsReader to ImageReader for symmetry with ImageWriter.

runtime/vm/raw_object.h

Index: runtime/vm/raw_object.h
diff --git a/runtime/vm/raw_object.h b/runtime/vm/raw_object.h
index de6956610cd3a20050848b32a031a5514a9280b2..9809aa85bb61e6f96246cbe47f31245262d66465 100644
--- a/runtime/vm/raw_object.h
+++ b/runtime/vm/raw_object.h
@@ -621,7 +621,7 @@ class RawObject {
   friend class InstanceAccumulator;        // GetClassId
   friend class RetainingPathVisitor;       // GetClassId
   friend class SkippedCodeFunctions;       // StorePointer
-  friend class InstructionsReader;         // tags_ check
+  friend class ImageReader;                // tags_ check
   friend class ImageWriter;
   friend class AssemblyImageWriter;
   friend class BlobImageWriter;
@@ -1227,7 +1227,7 @@ class RawInstructions : public RawObject {
   friend class MarkingVisitorBase;
   friend class SkippedCodeFunctions;
   friend class Function;
-  friend class InstructionsReader;
+  friend class ImageReader;
   friend class ImageWriter;
 };