Emit assembly instead of a blob for the instructions snapshot, and provide labels for the entry poi…

runtime/vm/datastream.h

Index: runtime/vm/datastream.h
diff --git a/runtime/vm/datastream.h b/runtime/vm/datastream.h
index bb46e4f49943fa81f37260320bfea45154460b9c..f47e822bd8ed4657e9af80f79bb73f862f0ff1a2 100644
--- a/runtime/vm/datastream.h
+++ b/runtime/vm/datastream.h
@@ -10,6 +10,7 @@
 #include "vm/allocation.h"
 #include "vm/exceptions.h"
 #include "vm/globals.h"
+#include "vm/os.h"
 
 namespace dart {
 
@@ -386,6 +387,12 @@ class WriteStream : public ValueObject {
     current_ += len;
   }
 
+  void Print(const char* format, ...) {
+    va_list args;
+    va_start(args, format);
+    VPrint(format, args);
+  }
+
  private:
   template<typename T>
   void Write(T value) {
@@ -426,6 +433,28 @@ class WriteStream : public ValueObject {
     ASSERT(end_ > *buffer_);
   }
 
+  void VPrint(const char* format, va_list args) {
+    // Measure.
+    va_list measure_args;
+    va_copy(measure_args, args);
+    intptr_t len = OS::VSNPrint(NULL, 0, format, measure_args);
+    va_end(measure_args);
+
+    // Alloc.
+    if ((end_ - current_) < (len + 1)) {
+      Resize(len + 1);
+    }
+    ASSERT((end_ - current_) >= (len + 1));
+
+    // Print.
+    va_list print_args;
+    va_copy(print_args, args);
+    OS::VSNPrint(reinterpret_cast<char*>(current_),
+                 len + 1, format, print_args);
+    va_end(print_args);
+    current_ += len;  // Not len + 1 to swallow the terminating NUL.
+  }
+
  private:
   uint8_t** const buffer_;
   uint8_t* end_;