Fix Clang warning about self assignment.
Fix Clang warning about self assignment.

Explicitly cast the variable to void rather than assign to self
to avoid warnings about unused variables.

This fixes the following Clang warning:

webkit/tools/test_shell/test_shell_main.cc:120:12: error: explicitly assigning a
      variable of type 'bool' to itself [-Wself-assign]
  ux_theme = ux_theme;
  ~~~~~~~~ ^ ~~~~~~~~
1 error generated.

(This is a new warning since Clang r122804.)

BUG=none
TEST=none

Review URL: http://codereview.chromium.org/6005012

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@70492 0039d316-1c4b-4281-b951-d872f2087c98

gavinp/chromium,Crystalnix/house-of-life-chromium,ropik/chromium,ropik/chromium,yitian134/chromium,ropik/chromium,Crystalnix/house-of-life-chromium,gavinp/chromium,gavinp/chromium,adobe/chromium,adobe/chromium,gavinp/chromium,adobe/chromium,Crystalnix/house-of-life-chromium,yitian134/chromium,adobe/chromium,ropik/chromium,yitian134/chromium,adobe/chromium,yitian134/chromium,ropik/chromium,ropik/chromium,Crystalnix/house-of-life-chromium,yitian134/chromium,adobe/chromium,ropik/chromium,yitian134/chromium,Crystalnix/house-of-life-chromium,yitian134/chromium,adobe/chromium,gavinp/chromium,Crystalnix/house-of-life-chromium,adobe/chromium,adobe/chromium,yitian134/chromium,Crystalnix/house-of-life-chromium,gavinp/chromium,Crystalnix/house-of-life-chromium,yitian134/chromium,adobe/chromium,Crystalnix/house-of-life-chromium,yitian134/chromium,gavinp/chromium,gavinp/chromium,Crystalnix/house-of-life-chromium,gavinp/chromium,adobe/chromium,gavinp/chromium,ropik/chromium,Crystalnix/house-of-life-chromium,ropik/chromium