Make built-ins strict mode conforming, and support a --use-strict flag.

src/debug-debugger.js

Index: src/debug-debugger.js
diff --git a/src/debug-debugger.js b/src/debug-debugger.js
index 120a2970079295a2a8752abbb0bc9e5df7048e92..91c70a027b413b2ae0982e9ccbbb6d85e7369867 100644
--- a/src/debug-debugger.js
+++ b/src/debug-debugger.js
@@ -26,14 +26,14 @@
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 // Default number of frames to include in the response to backtrace request.
-const kDefaultBacktraceLength = 10;
+var kDefaultBacktraceLength = 10;
 
-const Debug = {};
+var Debug = {};
 
 // Regular expression to skip "crud" at the beginning of a source line which is
 // not really code. Currently the regular expression matches whitespace and
 // comments.
-const sourceLineBeginningSkip = /^(?:\s*(?:\/\*.*?\*\/)*)*/;
+var sourceLineBeginningSkip = /^(?:\s*(?:\/\*.*?\*\/)*)*/;
 
 // Debug events which can occour in the V8 JavaScript engine. These originate
 // from the API include file debug.h.