New tabCapture.captureOffscreenTab API, initially for Presentation API 1UA mode

chrome/browser/extensions/api/tab_capture/offscreen_presentation.h

Index: chrome/browser/extensions/api/tab_capture/offscreen_presentation.h
diff --git a/chrome/browser/extensions/api/tab_capture/offscreen_presentation.h b/chrome/browser/extensions/api/tab_capture/offscreen_presentation.h
index 03ca5c22810b3cbf2daf8cb9073895912bec0fe8..fcd5d0ed2c719e2dda090d13e602dda5746bb1e5 100644
--- a/chrome/browser/extensions/api/tab_capture/offscreen_presentation.h
+++ b/chrome/browser/extensions/api/tab_capture/offscreen_presentation.h
@@ -20,6 +20,9 @@ class Profile;
 
 namespace extensions {
 
+// TODO(miu): This file and classes should be renamed, as this implementation
+// has expanded in scope to be used for all off-screen tabs.
+
 class OffscreenPresentation;  // Forward declaration.  See below.
 
 // Creates, owns, and manages all OffscreenPresentation instances created by the
@@ -31,7 +34,7 @@ class OffscreenPresentation;  // Forward declaration.  See below.
 // Usage:
 //
 //   OffscreenPresentationsOwner::Get(extension_contents)
-//       ->FindOrStartPresentation(start_url, presentation_id, size);
+//       ->StartPresentation(start_url, size);
 //
 // This class operates exclusively on the UI thread and so is not thread-safe.
 class OffscreenPresentationsOwner
@@ -44,14 +47,19 @@ class OffscreenPresentationsOwner
   static OffscreenPresentationsOwner* Get(
       content::WebContents* extension_web_contents);
 
-  // Find a presentation, keyed by |start_url| and |presentation_id|.  If found,
-  // return it.  Otherwise, instantiate a new one and return that.  If too many
-  // presentations have already been started, this method returns nullptr.
-  OffscreenPresentation* FindOrStartPresentation(
+  // Instantiate a new off-screen tab and navigate it to |start_url|.  The new
+  // tab's main frame will start out with the given |initial_size| in DIP
+  // coordinates.  If too many off-screen tabs have already been started, this
+  // method returns nullptr.
+  OffscreenPresentation* StartPresentation(
       const GURL& start_url,
-      const std::string& presentation_id,
       const gfx::Size& initial_size);
 
+  // Retrieve an existing instance by its ID.  If not found, this method returns
+  // nullptr.
+  OffscreenPresentation* FindByOffscreenTabId(
+      const std::string& offscreen_tab_id) const;
+
  protected:
   friend class OffscreenPresentation;
 
@@ -68,10 +76,8 @@ class OffscreenPresentationsOwner
 
   explicit OffscreenPresentationsOwner(content::WebContents* contents);
 
-  // Returns the OffscreenPresentation that matches the given |start_url| and
-  // |presentation_id|, or nullptr if not found.
-  OffscreenPresentation* FindPresentation(
-      const GURL& start_url, const std::string& presentation_id) const;
+  // Returns a unique, random ID that no other OffscreenPresentation has.
+  std::string CreateUniqueRandomId() const;
 
   content::WebContents* const extension_web_contents_;
   ScopedVector<OffscreenPresentation> presentations_;
@@ -104,7 +110,7 @@ class OffscreenPresentation : protected content::WebContentsDelegate,
   ~OffscreenPresentation() final;
 
   const GURL& start_url() const { return start_url_; }
-  const std::string& presentation_id() const { return presentation_id_; }
+  const std::string& id() const { return id_; }
 
   // The presentation page's WebContents instance.
   content::WebContents* web_contents() const {
@@ -184,8 +190,8 @@ class OffscreenPresentation : protected content::WebContentsDelegate,
   // current WebContents URL if navigations have occurred.
   const GURL start_url_;
 
-  // The presentation ID used to help uniquely identify this instance.
-  const std::string presentation_id_;
+  // An ID used to uniquely identify this instance.
+  const std::string id_;
 
   // A non-shared off-the-record profile based on the profile of the extension
   // background page.