Merge r185396 - GraphicsContext state stack wasting lots of memory wh…

…en empty.

<https://webkit.org/b/145817>

Reviewed by Geoffrey Garen.

Give the GraphicsContextState stack an inline capacity of 1, and make sure
to free any heap-allocated backing store when the stack goes empty.

The 1 is because HTMLCanvasElement keeps one "save" on the underlying
GraphicsContext at all times, and this prevents those canvases from always
sitting on an empty stack with 16 capacity.

This saves ~520 kB on cnet.com video pages.

* platform/graphics/GraphicsContext.cpp:
(WebCore::GraphicsContext::restore):
* platform/graphics/GraphicsContext.h:

Source/WebCore/ChangeLog

@@ -1,3 +1,23 @@
+2015-06-09  Andreas Kling  <akling@apple.com>
+
+        GraphicsContext state stack wasting lots of memory when empty.
+        <https://webkit.org/b/145817>
+
+        Reviewed by Geoffrey Garen.
+
+        Give the GraphicsContextState stack an inline capacity of 1, and make sure
+        to free any heap-allocated backing store when the stack goes empty.
+
+        The 1 is because HTMLCanvasElement keeps one "save" on the underlying
+        GraphicsContext at all times, and this prevents those canvases from always
+        sitting on an empty stack with 16 capacity.
+
+        This saves ~520 kB on cnet.com video pages.
+
+        * platform/graphics/GraphicsContext.cpp:
+        (WebCore::GraphicsContext::restore):
+        * platform/graphics/GraphicsContext.h:
+
 2015-06-09  Said Abou-Hallawa  <sabouhallawa@apple.com>
 
         SVG Fragment is not rendered if it is the css background image of an HTML element

Source/WebCore/platform/graphics/GraphicsContext.cpp

@@ -134,6 +134,11 @@ void GraphicsContext::restore()
     m_state = m_stack.last();
     m_stack.removeLast();
 
+    // Make sure we deallocate the state stack buffer when it goes empty.
+    // Canvas elements will immediately save() again, but that goes into inline capacity.
+    if (m_stack.isEmpty())
+        m_stack.clear();
+
     restorePlatformState();
 }
 

Source/WebCore/platform/graphics/GraphicsContext.h

@@ -555,7 +555,7 @@ namespace WebCore {
         GraphicsContextPlatformPrivate* m_data;
 
         GraphicsContextState m_state;
-        Vector<GraphicsContextState> m_stack;
+        Vector<GraphicsContextState, 1> m_stack;
         bool m_updatingControlTints;
         unsigned m_transparencyCount;
     };