Probe whether MFPlat.dll is present on Windows systems.

Not all versions of Windows 7 and later ship with Media Foundation DLLs. Instead of crashing while attempting to delay load the DLL, preemptively load the library and fail gracefully if we're unable to do so.

BUG=339678

Review URL: https://codereview.chromium.org/151993002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@248586 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 248586
Follow-up changes to Android certificate verification logic.

- Handle devices without an "AndroidCAStore" KeyStore. Add a histogram to
  record when this happens.
- Remove resolved TODO.
- Unnecessary exception check (relevant function already CalledByNative, not
  CalledByNativeUnchecked)

BUG=116838
TEST=none

Review URL: https://codereview.chromium.org/144153002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@248587 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 248587