Update V8 to r3431 as required by WebKit r51976.

Change-Id: I567392c3f8c0a0d5201a4249611ac4ccf468cd5b
diff --git a/src/disassembler.cc b/src/disassembler.cc
index e2f908d..524dbe6 100644
--- a/src/disassembler.cc
+++ b/src/disassembler.cc
@@ -74,7 +74,7 @@
   }
 
   if (code_ != NULL) {
-    int offs = pc - code_->instruction_start();
+    int offs = static_cast<int>(pc - code_->instruction_start());
     // print as code offset, if it seems reasonable
     if (0 <= offs && offs < code_->instruction_size()) {
       OS::SNPrintF(buffer, "%d  (%p)", offs, pc);
@@ -289,7 +289,7 @@
   }
 
   delete it;
-  return pc - begin;
+  return static_cast<int>(pc - begin);
 }