Move plugin loading logic from SubframeLoader to HTMLPluginImageElement

BUG=none

Review URL: https://chromiumcodereview.appspot.com/21069004

git-svn-id: svn://svn.chromium.org/blink/trunk@155125 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Move the WTF::SHA1 unit test to wtf/SHA1Test.cpp.

Previously it was run when its constructor was called in debug builds.
We have better ways of running unit tests now.

BUG=265623

Review URL: https://chromiumcodereview.appspot.com/21087004

git-svn-id: svn://svn.chromium.org/blink/trunk@155126 bbb929c8-8fbe-4397-9dbb-9b2b20218538