Tweak the description of the BackForwardCache feature.

Fix some grammar problems. Also mark "unload" as a non-translatable
term.

Change-Id: I422a2ad871a202c8576ad72b0166e8a4107dedab
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2342536
Commit-Queue: Fergal Daly <fergal@chromium.org>
Reviewed-by: Rakina Zata Amni <rakina@chromium.org>
Reviewed-by: Julian Pastarmov <pastarmovj@chromium.org>
Reviewed-by: Alexander Timin <altimin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#797250}

components/policy/resources/policy_templates.json

@@ -22730,16 +22730,12 @@ If you disable this policy, web page scrolling to specific text fragments via UR
       'id': 758,
       'caption': '''Control the <ph name="PRODUCT_NAME">BackForwardCache</ph> feature.''',
       'tags': [],
-      'desc': '''When enabled the <ph name="PRODUCT_NAME">BackForwardCache</ph> feature causes web pages to be preserved in its current state (document tree, script, etc.) into the back-forward cache when navigated away from the page.
-          If we navigated back to the page, the page will be restored from the back-forward cache, showing it in the state it was in when cached before.
+      'desc': '''When enabled the <ph name="PRODUCT_NAME">BackForwardCache</ph> feature allows the use of the back-forward cache. When navigating away from a page, its current state (document tree, script, etc.) may be preserved in the back-forward cache. If the browser navigates back to the page, the page may be restored from the back-forward cache and displayed in the state it was in before being cached.
 
-          This feature might break some websites that does not expect itself to
-          get cached, particularly websites that depend on unload handlers being
-          fired when navigated away from the page, as the unload event will
-          not be dispatched when navigated away from a page and it gets saved
-          in the back-forward cache.
+          This feature might cause issues for some websites that do not expect this caching. In particular, some websites depend on the "<ph name="UNLOAD_HANDLER_NAME">unload</ph>" event being dispatched when the browser navigates away from the page. The "<ph name="UNLOAD_HANDLER_NAME">unload</ph>" event will not be dispatched if the page enters the back-forward cache.
 
-          If this policy is set to enabled or not set, the <ph name="PRODUCT_NAME">BackForwardCache</ph> feature will be enabled.
+          If this policy is set to enabled or not set,
+          the <ph name="PRODUCT_NAME">BackForwardCache</ph> feature will be enabled.
 
           If this policy is set to disabled then the feature will be force disabled.
           ''',