MD Extensions: remove section header from shortcuts view

It's duplicative with input validation messaging and this was requested
by designer bettes@ during a polish pass.

Bug: 787227
Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation
Change-Id: I1e9f3267b8a62f886ebb0b6ff93d59f6d1006aa2
Reviewed-on: https://chromium-review.googlesource.com/786398
Commit-Queue: Dan Beam (no longer on Chrome) <dbeam@chromium.org>
Reviewed-by: Demetrios Papadopoulos <dpapad@chromium.org>
Cr-Commit-Position: refs/heads/master@{#519585}

chrome/app/md_extensions_strings.grdp

@@ -203,17 +203,11 @@
     Type a shortcut
   </message>
 <if expr="is_macosx">
-  <message name="IDS_MD_EXTENSIONS_SHORTCUT_INSTRUCTIONS" desc="Instructions explaining that shortcuts must start with either the Control, Alt, or Command key.">
-    Shortcuts must start with Ctrl, Alt, or Command
-  </message>
   <message name="IDS_MD_EXTENSIONS_INCLUDE_START_MODIFIER" desc="Error message explaining that shortcuts must start with either the Control, Alt, or Command key.">
     Include Ctrl, Alt, or Command
   </message>
 </if>
 <if expr="chromeos">
-  <message name="IDS_MD_EXTENSIONS_SHORTCUT_INSTRUCTIONS" desc="Instructions explaining that shortcuts must start with either the Control, Alt, or Search key.">
-    Shortcuts must start with Ctrl, Alt, or Search
-  </message>
   <message name="IDS_MD_EXTENSIONS_INCLUDE_START_MODIFIER" desc="Error message explaining that shortcuts must start with either the Control, Alt, or Search key.">
     Include Ctrl, Alt, or Search
   </message>
@@ -224,9 +218,6 @@
   </message>
 </if>
 <if expr="not is_macosx and not chromeos">
-  <message name="IDS_MD_EXTENSIONS_SHORTCUT_INSTRUCTIONS" desc="Instructions explaining that shortcuts must start with either the Control key or the Alt key.">
-    Shortcuts must start with either Ctrl or Alt
-  </message>
   <message name="IDS_MD_EXTENSIONS_INCLUDE_START_MODIFIER" desc="Error message explaining that shortcuts must start with either the Control key or the Alt key.">
     Include either Ctrl or Alt
   </message>

chrome/browser/resources/md_extensions/keyboard_shortcuts.html

@@ -19,7 +19,6 @@
         height: 100%;
       }
 
-      #instructions,
       .shortcut-card {
         margin: 0 auto 16px auto;
         max-width: var(--card-max-width);
@@ -27,10 +26,6 @@
         width: 90%;
       }
 
-      #instructions {
-        @apply --cr-title-text;
-      }
-
       .shortcut-card {
         @apply --cr-primary-text;
         @apply --shadow-elevation-2dp;
@@ -93,7 +88,6 @@
       }
     </style>
     <div id="container">
-      <div id="instructions">$i18n{shortcutInstructions}</div>
       <template is="dom-repeat" items="[[calculateShownItems_(items.*)]]">
         <div class="shortcut-card">
           <div class="card-title">

chrome/browser/ui/webui/extensions/extensions_ui.cc

@@ -264,8 +264,6 @@ content::WebUIDataSource* CreateMdExtensionsSource() {
                              IDS_MD_EXTENSIONS_SHORTCUT_SCOPE_IN_CHROME);
   source->AddLocalizedString("shortcutTypeAShortcut",
                              IDS_MD_EXTENSIONS_TYPE_A_SHORTCUT);
-  source->AddLocalizedString("shortcutInstructions",
-                             IDS_MD_EXTENSIONS_SHORTCUT_INSTRUCTIONS);
   source->AddLocalizedString("shortcutIncludeStartModifier",
                              IDS_MD_EXTENSIONS_INCLUDE_START_MODIFIER);
   source->AddLocalizedString("shortcutTooManyModifiers",