Rename InstructionsReader to ImageReader for symmetry with ImageWriter.

runtime/vm/snapshot.cc

Index: runtime/vm/snapshot.cc
diff --git a/runtime/vm/snapshot.cc b/runtime/vm/snapshot.cc
index d720d0ef67efd9d017814adfff8599e7f16c44bf..e81340d10d6927798871ab1b6c6ca5746e4e21fd 100644
--- a/runtime/vm/snapshot.cc
+++ b/runtime/vm/snapshot.cc
@@ -1066,7 +1066,7 @@ void BlobImageWriter::WriteText(WriteStream* clustered_stream, bool vm) {
 }
 
 
-RawInstructions* InstructionsReader::GetInstructionsAt(int32_t offset) {
+RawInstructions* ImageReader::GetInstructionsAt(int32_t offset) {
   ASSERT(Utils::IsAligned(offset, OS::PreferredCodeAlignment()));
 
   RawInstructions* result = reinterpret_cast<RawInstructions*>(
@@ -1078,7 +1078,7 @@ RawInstructions* InstructionsReader::GetInstructionsAt(int32_t offset) {
 }
 
 
-RawObject* InstructionsReader::GetObjectAt(int32_t offset) {
+RawObject* ImageReader::GetObjectAt(int32_t offset) {
   ASSERT(Utils::IsAligned(offset, kWordSize));
 
   RawObject* result = reinterpret_cast<RawObject*>(