Create specialized code stubs for PixelArray loads.

src/runtime.cc

Index: src/runtime.cc
diff --git a/src/runtime.cc b/src/runtime.cc
index 96d07a859b296b5223d7355f56d1fbb591535b17..781ac0c7c3e0092893331e4496416f837015f454 100644
--- a/src/runtime.cc
+++ b/src/runtime.cc
@@ -3487,8 +3487,10 @@ static MaybeObject* Runtime_KeyedGetProperty(Arguments args) {
     HandleScope scope;
     Handle<String> str = args.at<String>(0);
     int index = Smi::cast(args[1])->value();
-    Handle<Object> result = GetCharAt(str, index);
-    return *result;
+    if (index >= 0 && index < str->length()) {
+      Handle<Object> result = GetCharAt(str, index);
+      return *result;
+    }
   }
 
   // Fall back to GetObjectProperty.