screen_ui: Use std::string in DrawTextLine() and siblings.

Test: mmma -j bootable/recovery
Test: Build and boot into recovery image on angler. Check the UI.
Test: Repeat the same test on devices using wearable UI.
Change-Id: I1a67ff4ae8de4d7a8dc66326cf07f95c89e95152
diff --git a/vr_ui.cpp b/vr_ui.cpp
index a58c99e..b1ef646 100644
--- a/vr_ui.cpp
+++ b/vr_ui.cpp
@@ -39,9 +39,9 @@
   gr_texticon(x - kStereoOffset + ScreenWidth(), y, surface);
 }
 
-int VrRecoveryUI::DrawTextLine(int x, int y, const char* line, bool bold) const {
-  gr_text(gr_sys_font(), x + kStereoOffset, y, line, bold);
-  gr_text(gr_sys_font(), x - kStereoOffset + ScreenWidth(), y, line, bold);
+int VrRecoveryUI::DrawTextLine(int x, int y, const std::string& line, bool bold) const {
+  gr_text(gr_sys_font(), x + kStereoOffset, y, line.c_str(), bold);
+  gr_text(gr_sys_font(), x - kStereoOffset + ScreenWidth(), y, line.c_str(), bold);
   return char_height_ + 4;
 }