[Android] Add CSP support.

Enable CSP control for packaged app by parse CSP content from
manifest.json and adding the CSP content into the http response
header.

Bug=https://crosswalk-project.org/jira/browse/XWALK-692
[Android] Add test for CSP support.

The test set the manifest field script-src with 'self' or
'unsafe-inline' values to disallow/allow change page titles
with the diferent CSP settings.

For embedded client test:
1. install XWalkRuntimeClientEmbeddedShell.apk
2. python build/android/test_runner.py instrumentation \
--test-apk=XWalkRuntimeClientEmbeddedTest -v -f \
testCSP

For shared client test:
1. install XWalkRuntimeLib.apk
2. install XWalkRuntimeClientShell.apk
3. python build/android/test_runner.py instrumentation \
--test-apk=XWalkRuntimeClientTest -v -f testCSP
Merge pull request #1500 from gaochun/csp

[Android] CSP support.