Synchronize with r15701.

ChangeLog

+2013-07-17: Version 3.20.6
+
+        Try to remove invalidated stubs before falling back to checking the
+        constant state (Chromium issue 260585).
+
+        Fixed gyp_v8 to work with use_system_icu=1 (issue 2475).
+
+        Fixed sloppy-mode 'const' under Harmony flag (Chromium issue 173361).
+
+        Use internal array as API function cache  (Chromium issue 260106).
+
+        Fixed possible stack overflow in range analysis
+        (Chromium issue 259452).
+
+        Performance and stability improvements on all platforms.
+
+
+2013-07-15: Version 3.20.5
+
+        Ensured that the length of frozen arrays is immutable
+        (issue 2711, Chromium issue 259548).
+
+        Performance and stability improvements on all platforms.
+
+
+2013-07-10: Version 3.20.4
+
+        Fixed garbage-collection issue that causes a crash on ARM
+        (Chromium issue 254570)
+
+        Performance and stability improvements on all platforms.
+
+
 2013-07-08: Version 3.20.3
 
         Performance and stability improvements on all platforms.
 
 
 2013-07-05: Version 3.20.2
 
         Remove deprecated heap profiler methods from V8 public API
 
         Mark i18n functions as native and set proper names
@@ skipping 5568 matching lines @@
         setting break points in them.
 
 
 2008-07-03: Version 0.1.0
 
         Initial export.
 
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