DevTools: make flame chart a web component.

Source/devtools/front_end/helpScreen.css

 .help-window-outer {
     position: absolute !important;
     top: 0;
     left: 0;
     right: 0;
     bottom: 0;
     z-index: 2000;
 }
 
 .help-window-main {
@@ skipping 65 matching lines @@
 .help-close-button {
     position: absolute;
     top: 8px;
     right: 8px;
 }
 
 body.dock-to-bottom .help-content {
     margin-bottom: 8px;
 }
 
-body.platform-mac .help-window-main .tabbed-pane-header-contents {
+.platform-mac .help-window-main .tabbed-pane-header-contents {
     margin-left: 27px;
 }
 
-body.platform-mac .help-window-main .help-window-title {
+.platform-mac .help-window-main .help-window-title {
     margin-left: 18px;
 }
 
 .help-container {
     width: 100%;
     -webkit-user-select: auto;
     -webkit-column-width: 470px;
 }
 
-body.platform-mac .settings-tab .help-container {
+.platform-mac .settings-tab .help-container {
     -webkit-column-width: 430px;
 }
 
-body.platform-mac .help-container {
+.platform-mac .help-container {
     -webkit-column-width: 361px;
 }
 
 .help-no-columns {
     -webkit-column-width: initial !important;
 }
 
 .help-block {
     display: block;
     padding-bottom: 9px;
     width: 470px;
     -webkit-column-break-inside: avoid;
 }
 
-body.platform-mac .settings-tab .help-block {
+.platform-mac .settings-tab .help-block {
     width: 430px;
 }
 
 .settings-tab.help-container {
     -webkit-column-width: 410px;
 }
 
 .settings-tab .help-block {
     width: 410px;
     margin-left: 20px;
 }
 
 .settings-tab .field-error-message {
     color: DarkRed;
     height: 0px; /* Avoid changing element height when content is set. */
 }
 
 .help-line {
     padding-bottom: 5px;
     margin-bottom: 5px;
 }
 
 .help-key-cell {
     display: inline-block;
     width: 270px;
     text-align: right;
 }
 
-body.platform-mac .help-key-cell {
+.platform-mac .help-key-cell {
     width: 151px;
 }
 
 .help-cell {
     display: inline-block;
     width: 200px;
     vertical-align: middle;
 }
 
 .help-section-title {
     font-size: 120%;
 }
 
 .help-key {
     padding: 0.1em 0.6em;
     border: 1px solid #ccc;
     font-size: 11px;
     background-color: #f7f7f7;
     color: #333;
     box-shadow: 0 1px 0px rgba(0, 0, 0, 0.2), 0 0 0 2px #ffffff inset;
     border-radius: 3px;
     display: inline-block;
     margin: 0 0.1em;
     text-shadow: 0 1px 0 #fff;
     line-height: 1.5;
     white-space: nowrap;
 }
 
-body.platform-mac .help-key {
+.platform-mac .help-key {
     font-family: Lucida Grande, sans-serif;
 }
 
 .help-combine-keys,
 .help-key-delimiter {
     font-size: 9px;
 }
 
 .help-combine-keys {
     margin: 0 0.3em;
@@ skipping 451 matching lines @@
     display: none;
 }
 
 .settings-experiment-hidden label {
     background-color: #ddd;
 }
 
 .settings-developer-mode .settings-experiment-hidden {
     display: block;
 }