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This is the first patch to separate JNI registration with initialization, currently, we have JNI_OnLoad defined multiple places which has a lot of
duplicated code and JNI registration and initialization are mixed;

This patch
- Added JNIOnLoadDelegate class for each component  specific initialization.
- Added base::android::OnJNIOnLoad() to call a list of delegates
- Migrate testing, content_shell, chrome_shell.

BUG=447393
TBR=thakis

Review URL: https://codereview.chromium.org/864563002

Cr-Commit-Position: refs/heads/master@{#313592}