Simplify ScreenCapturer interface.

media/video/capture/screen/screen_capturer.h

Index: media/video/capture/screen/screen_capturer.h
diff --git a/media/video/capture/screen/screen_capturer.h b/media/video/capture/screen/screen_capturer.h
index 1dc2330ac6d62fb07e1ddbce6bacbe72d5feb404..5673d2891bd3a6b2813a50a2ce69e93ac290735e 100644
--- a/media/video/capture/screen/screen_capturer.h
+++ b/media/video/capture/screen/screen_capturer.h
@@ -11,7 +11,6 @@
 #include "base/shared_memory.h"
 #include "media/base/media_export.h"
 #include "media/video/capture/screen/shared_buffer.h"
-#include "third_party/skia/include/core/SkRegion.h"
 
 namespace media {
 
@@ -27,25 +26,13 @@ class SharedBuffer;
 //     This is when pre-capture steps are executed, such as flagging the
 //     display to prevent it from sleeping during a session.
 //
-// (2) InvalidateRegion
-//     This is an optional step where regions of the screen are marked as
-//     invalid. Some platforms (Windows, for now) won't use this and will
-//     instead calculate the diff-regions later (in step (2). Other
-//     platforms (Mac) will use this to mark all the changed regions of the
-//     screen. Some limited rect-merging (e.g., to eliminate exact
-//     duplicates) may be done here.
-//
-// (3) CaptureFrame
+// (2) CaptureFrame
 //     This is where the bits for the invalid rects are packaged up and sent
 //     to the encoder.
 //     A screen capture is performed if needed. For example, Windows requires
 //     a capture to calculate the diff from the previous screen, whereas the
 //     Mac version does not.
 //
-// (4) Stop
-//     This is when post-capture steps are executed, such as releasing the
-//     assertion that prevents the display from sleeping.
-//
 // Implementation has to ensure the following guarantees:
 // 1. Double buffering
 //    Since data can be read while another capture action is happening.
@@ -92,12 +79,6 @@ class MEDIA_EXPORT ScreenCapturer {
   // valid until Stop() is called.
   virtual void Start(Delegate* delegate) = 0;
 
-  // Called at the end of a capturing session.
-  virtual void Stop() = 0;
-
-  // Invalidates the specified region.
-  virtual void InvalidateRegion(const SkRegion& invalid_region) = 0;
-
   // Captures the screen data associated with each of the accumulated
   // dirty region. When the capture is complete, the delegate is notified even
   // if the dirty region is empty.