Don't toggle caret browsing on Mac unless web contents has focus.

Pressing F7 to toggle caret browsing was interfering with a Japanese
IME on Mac, but only when the omnibox has focus. There were no
conflicts when focus is in a web page. So to work around this issue,
ignore the F7 shortcut when focus is

It turns out Firefox has the same behavior: it ignores the F7 toggle
when focus is in its address bar. So that's good motivation that this
is the right fix.

There hasn't been any feedback about a similar issue on other
platforms, so scoping the fix to just Mac.

Bug: 1138475
Change-Id: I19b5ccaf9aec0b46c76e241887af60b0180a7338
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2472897Reviewed-by: Elly Fong-Jones <ellyjones@chromium.org>
Commit-Queue: Dominic Mazzoni <dmazzoni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#817162}

chrome/browser/ui/browser_commands.cc

@@ -1536,6 +1536,20 @@ bool CanViewSource(const Browser* browser) {
 }
 
 void ToggleCaretBrowsing(Browser* browser) {
+#if defined(OS_MAC)
+  // On Mac, ignore the keyboard shortcut unless web contents is focused,
+  // because the keyboard shortcut interferes with a Japenese IME when the
+  // omnibox is focused.  See https://crbug.com/1138475
+  WebContents* web_contents =
+      browser->tab_strip_model()->GetActiveWebContents();
+  if (!web_contents)
+    return;
+
+  content::RenderWidgetHostView* rwhv = web_contents->GetRenderWidgetHostView();
+  if (!rwhv || !rwhv->HasFocus())
+    return;
+#endif  // defined(OS_MAC)
+
   PrefService* prefService = browser->profile()->GetPrefs();
   bool enabled = prefService->GetBoolean(prefs::kCaretBrowsingEnabled);