imf: Handle sentence autocap mode.

In a previous CL [1], we fixed a bug with autocapitalize="off". However,
we forgot to handle autocapitalize="sentence", because in the old code,
"sentence" was automatically handled as a default case, but we changed
the default behaviour to "none", so sentence was treated as none.

[1] https://chromium-review.googlesource.com/c/chromium/src/+/1762254

Bug: 995703
Change-Id: Id1e634386676c62270d00f365004bebbc170538a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1850673Reviewed-by: Shu Chen <shuchen@chromium.org>
Commit-Queue: Darren Shen <shend@chromium.org>
Cr-Commit-Position: refs/heads/master@{#704435}

chrome/browser/extensions/api/input_ime/input_ime_api_chromeos.cc

@@ -354,6 +354,8 @@ class ImeObserverChromeOS : public ui::ImeObserver {
       return input_method_private::AUTO_CAPITALIZE_TYPE_CHARACTERS;
     if (flags & ui::TEXT_INPUT_FLAG_AUTOCAPITALIZE_WORDS)
       return input_method_private::AUTO_CAPITALIZE_TYPE_WORDS;
+    if (flags & ui::TEXT_INPUT_FLAG_AUTOCAPITALIZE_SENTENCES)
+      return input_method_private::AUTO_CAPITALIZE_TYPE_SENTENCES;
 
     // Autocapitalize flag may be missing for native text fields.
     // See https://crbug.com/1002713.