Sanitize HTML for Android Email and the EML viewer
Sanitize HTML for Android Email and the EML viewer

b/14567151

This check-in introduces the sanitizer class and the necessary build
changes to compile it. A sibling checkin will actually call it.

Change-Id: I6b6a15b31a5b6be4fcd666a269dd2ccbe9e9fd50

geekboxzone/mmallow_external_owasp_sanitizer,geekboxzone/mmallow_external_owasp_sanitizer,android-ia/platform_external_owasp_sanitizer,Omegaphora/external_owasp_sanitizer,android-ia/platform_external_owasp_sanitizer,CyanogenMod/android_external_owasp_sanitizer,geekboxzone/mmallow_external_owasp_sanitizer,Omegaphora/external_owasp_sanitizer,CyanogenMod/android_external_owasp_sanitizer,geekboxzone/lollipop_external_owasp_sanitizer,geekboxzone/lollipop_external_owasp_sanitizer,Omegaphora/external_owasp_sanitizer,geekboxzone/lollipop_external_owasp_sanitizer,android-ia/platform_external_owasp_sanitizer