Revise tooltip content for screen sharing per suggestion from UX writer.

UX and PM think it's better to say "This tab is sharing your screen.".
Also fixed a typo in desc.

Bug:859981

TBR=rockot@chromium.org

Change-Id: I503ab2ce47190ed1069e99a58eaa01c001558a8e
Reviewed-on: https://chromium-review.googlesource.com/1169540Reviewed-by: Weiyong Yao <braveyao@chromium.org>
Commit-Queue: Weiyong Yao <braveyao@chromium.org>
Cr-Commit-Position: refs/heads/master@{#581934}

chrome/app/generated_resources.grd

@@ -8574,8 +8574,8 @@ Please help our engineers fix this problem. Tell us what happened right before y
       <message name="IDS_TOOLTIP_TAB_ALERT_STATE_PIP_PLAYING" desc="Extra tool tip text, when tab is playing a video in Picture-in-Picture.">
         This tab is playing a video in picture-in-picture mode.
       </message>
-      <message name="IDS_TOOLTIP_TAB_ALERT_STATE_DESKTOP_CAPTURING" desc="Extra tool tip text, when the tab is caturing desktop contents.">
-        This tab is sharing your desktop content.
+      <message name="IDS_TOOLTIP_TAB_ALERT_STATE_DESKTOP_CAPTURING" desc="Extra tool tip text, when the tab is capturing desktop contents.">
+        This tab is sharing your screen.
       </message>
 
       <!-- Tab accessibility labels -->

chrome/app/generated_resources_grd/IDS_TOOLTIP_TAB_ALERT_STATE_DESKTOP_CAPTURING.png.sha1

+7d3b067c3f60b572dfc831350f66c05c3a112864
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