[Modal] Implement disableScrollLock property

[fltonii]

Is there any documentation regarding this functionality out there? I saw a mention of it in the modal api reference but can't find when/how to use it.

[oliviertassinari]

We could add a property for this.

[Sojborg]

I also need to be able to disableScrollLock. Sounds good with a property for this.

[oliviertassinari]

@Sojborg If you want to give it a shot, it shouldn't be harder than:

 --- a/packages/material-ui/src/Modal/Modal.js
+++ b/packages/material-ui/src/Modal/Modal.js
@@ -213,6 +213,7 @@ class Modal extends React.Component {
       disableEscapeKeyDown,
       disablePortal,
       disableRestoreFocus,
+      disableScrollLock,
       hideBackdrop,
       innerRef,
       keepMounted,
@@ -354,6 +355,10 @@ Modal.propTypes = {
    */
   disableRestoreFocus: PropTypes.bool,
   /**
+   * Disable the scroll lock behavior.
+   */
+  disableScrollLock: PropTypes.bool,
+  /**
    * If `true`, the backdrop is not rendered.
    */
   hideBackdrop: PropTypes.bool,
@@ -412,6 +417,7 @@ Modal.defaultProps = {
   disableEscapeKeyDown: false,
   disablePortal: false,
   disableRestoreFocus: false,
+  disableScrollLock: false,
   hideBackdrop: false,
   keepMounted: false,
   // Modals don't open on the server so this won't conflict with concurrent requests.
diff --git a/packages/material-ui/src/Modal/ModalManager.js b/packages/material-ui/src/Modal/ModalManager.js
index 0a381abb9..f6334de0e 100644
--- a/packages/material-ui/src/Modal/ModalManager.js
+++ b/packages/material-ui/src/Modal/ModalManager.js
@@ -75,10 +75,9 @@ function removeContainerStyle(data) {
  */
 class ModalManager {
   constructor(options = {}) {
-    const { hideSiblingNodes = true, handleContainerOverflow = true } = options;
+    const { hideSiblingNodes = true } = options;

     this.hideSiblingNodes = hideSiblingNodes;
-    this.handleContainerOverflow = handleContainerOverflow;

     // this.modals[modalIdx] = modal
     this.modals = [];
@@ -130,7 +129,7 @@ class ModalManager {
     const containerIdx = findIndexOf(this.data, item => item.modals.indexOf(modal) !== -1);
     const data = this.data[containerIdx];

-    if (!data.style && this.handleContainerOverflow) {
+    if (!data.style && !modal.props.disableScrollLock) {
       setContainerStyle(data);
     }
   }
@@ -150,7 +149,7 @@ class ModalManager {

     // If that was the last modal in a container, clean up the container.
     if (data.modals.length === 0) {
-      if (this.handleContainerOverflow) {
+      if (!data.style && !modal.props.disableScrollLock) {
         removeContainerStyle(data);
       }