win: Also look in PROGRAMW6432 for cdb

This is necessary for 64 bit tools installed on a 64 bit OS, but with
the tests run from a 32 bit Python. (sigh)

Doesn't happen on bots, but comes up occasionally testing on VMs.

R=mark@chromium.org

Review URL: https://codereview.chromium.org/1425153003 .

snapshot/win/end_to_end_test.py

@@ -41,6 +41,7 @@ def CleanUpTempDirs():
 def FindInstalledWindowsApplication(app_path):
   search_paths = [os.getenv('PROGRAMFILES(X86)'),
                   os.getenv('PROGRAMFILES'),
+                  os.getenv('PROGRAMW6432'),
                   os.getenv('LOCALAPPDATA')]
   search_paths += os.getenv('PATH', '').split(os.pathsep)