[Extensions] Remove uses of deprecated v8::String::New()

As announced in
http://permalink.gmane.org/gmane.comp.web.chromium.devel/47781, Chromium
will change to break when using deprecated V8 functions. Since the
non-deprecated versions are already available for us, we can start to
use them before we hit the breakage.

This patch changes our uses of v8::String::New() to the corresponding
new functions that take the v8::Isolate* parameter.
[Extensions] Remove uses of deprecated v8::Persistent::Dispose()/Clear()

As announced in
http://permalink.gmane.org/gmane.comp.web.chromium.devel/47781, Chromium
will change to break when using deprecated V8 functions. Since the
non-deprecated versions are already available for us, we can start to
use them before we hit the breakage.

This patch replaces the uses of Dispose()/Clear() with the
v8::Persistent::Reset() function.
[Extensions] Remove uses of deprecated v8::HandleScope::Close()

As announced in
http://permalink.gmane.org/gmane.comp.web.chromium.devel/47781, Chromium
will change to break when using deprecated V8 functions. Since the
non-deprecated versions are already available for us, we can start to
use them before we hit the breakage.

The functionality provided by v8::HandleScope::Close() is now provided
by the v8::EscapableHandleScope.
Merge pull request #1238 from cmarcelo/fix-v8-deprecated-usages

[Extensions] Fix v8 deprecated usages