Merge V8 at 2.5.9.19

Pull in the latest V8 for various stability fixes.

Note that this deviates from the Chromium 9.0.597.x branch.

Bug: 3483676
Change-Id: I06d94f1d178d76395fe437a9ac01a4c71f0fada9
diff --git a/src/arm/macro-assembler-arm.h b/src/arm/macro-assembler-arm.h
index 8bd134c..27d1671 100644
--- a/src/arm/macro-assembler-arm.h
+++ b/src/arm/macro-assembler-arm.h
@@ -673,6 +673,9 @@
   // Abort execution if argument is a smi. Used in debug code.
   void AbortIfSmi(Register object);
 
+  // Abort execution if argument is a string. Used in debug code.
+  void AbortIfNotString(Register object);
+
   // ---------------------------------------------------------------------------
   // String utilities