Replace tab character with spaces for Aura tooltips

When EnableAuraTooltipsOnWindows was enabled, HTML title attributes and
other content that display tooltips started rendering a box instead of
whitespace for a tab character.

This change replaces tab characters with six spaces, approximating the
rendering of pre-EnableAuraTooltipsOnWindows display and that of other
browsers.

Bug: 993100
Change-Id: Ib0a39850bfd13b73a960828cd465cc965e6a713d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1834889Reviewed-by: Michael Wasserman <msw@chromium.org>
Reviewed-by: Cliff Smolinsky <cliffsmo@microsoft.com>
Commit-Queue: Eric Lawrence [MSFT] <ericlaw@microsoft.com>
Cr-Commit-Position: refs/heads/master@{#703321}

ui/views/corewm/tooltip_aura.cc

@@ -121,7 +121,13 @@ class TooltipAura::TooltipView : public views::View {
 
   void SetText(const base::string16& text) {
     render_text_->SetHorizontalAlignment(gfx::ALIGN_TO_HEAD);
-    render_text_->SetText(text);
+
+    // Replace tabs with whitespace to avoid placeholder character rendering
+    // where previously it did not. crbug.com/993100
+    base::string16 newText(text);
+    base::ReplaceChars(newText, base::ASCIIToUTF16("\t"),
+                       base::ASCIIToUTF16("        "), &newText);
+    render_text_->SetText(newText);
     SchedulePaint();
   }