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This change fixes an issue with the delayed initialization of the
spellcheck service (a feature that in Chromium is currently behind the
WinDelaySpellcheckServiceInit feature flag). While the first click in
the editable content indeed initializes the spellcheck service by
loading dictionaries, it does not guarantee a successful spell check
request. Spelling may not be checked until further typing or focusing
in a different editable element. If the text is long enough
(multilined?), then a single click works.

The bug is caused by a race condition in the mojo calls from the
browser to the renderer process. There is no guarantee that the
callback to the renderer process when InitializeDictionaries completes
will be invoked in the renderer process after the call to
SpellCheck::Initialize that results from the browser method
SpellcheckService::InitForRenderer. If the first call wins the race,
no spellchecking will occur because the spellcheck provider thinks
there are no dictionaries available and does not check spelling.

Mojo does not guarantee ordering in separate message pipes, which
the SpellChecker and SpellCheckHost interfaces comprise. One fix that
I considered was to make these associated interfaces that share a
single channel between the browser and renderer processes. But I
believe this risks breaking other platforms. So the fix I have
here instead ensures that when the InitializeDictionaries callback is
received in the renderer, SpellCheck::Initialize is called with the
list of dictionaries provided by the browser process.

Test coverage is provided by a browser test based on the original test
that caught this bug (ChromeSitePerProcessTest.OOPIFSpellCheckTest):
ChromeSitePerProcessSpellCheckTestDelayInit.OOPIFSpellCheckTest. The
HTML source for this browser test contains just a snippet of editable
content, so putting focus in it to invoke spellchecking and initialize
the spellcheck service on demand exposed the issue.

Bug: 1103847
Change-Id: I809e4aef3d51808d222012ddd0c0b46e3d57098a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2335028Reviewed-by: Ken Buchanan <kenrb@chromium.org>
Reviewed-by: Rouslan Solomakhin <rouslan@chromium.org>
Reviewed-by: Guillaume Jenkins <gujen@google.com>
Commit-Queue: Bruce Long <brlong@microsoft.com>
Cr-Commit-Position: refs/heads/master@{#796789}