Implement find in page support for top level BrowserPlugins.
Right now BrowserPlugins don't handle find in page. This CL adds support for find in page in MIMEHandlerView BrowserPlugin instances.
Find in page is only handled for "full page" plugins, that is when the BrowserPlugin as loaded at the top level. The reason is because supporting find in embedded BrowserPlugins would require recursively searching which is far more complicated to implement and we (jam@, fsamuel@) have decided to defer implementing for the time being.
Detecting whether the BrowserPlugin is loaded at the top level requires detecting whether the main frame is a "plugin document" in blink, which needs to be sent to the browser from the renderer. It isn't sufficient to determine whether the BrowserPlugin is merely loaded in the main frame, because it may be <embed>ed inside a html document in the main frame. In that case we don't want find in page to search the document.
BUG=303491
Review URL: https://codereview.chromium.org/597753003
Cr-Commit-Position: refs/heads/master@{#299358}
14 files changed
