Revert r160178 "Remove code in Editor::rangeOfString() that unnecessarily resets the searchRange after the first find operation."
Revert r160178 "Remove code in Editor::rangeOfString() that unnecessarily resets the searchRange after the first find operation."

It breaks FindInPageControllerTest.IncognitoFindNextSecret:
http://build.chromium.org/p/chromium.webkit/builders/Linux%20Tests/builds/31909/steps/browser_tests/logs/stdio

TBR=jsbell
BUG=

Review URL: https://codereview.chromium.org/34473003

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@160222 bbb929c8-8fbe-4397-9dbb-9b2b20218538

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