Added const to image parameters for ImageButton class.

views/controls/button/image_button.cc

Index: views/controls/button/image_button.cc
===================================================================
--- views/controls/button/image_button.cc	(revision 48732)
+++ views/controls/button/image_button.cc	(working copy)
@@ -29,13 +29,13 @@
 ImageButton::~ImageButton() {
 }
 
-void ImageButton::SetImage(ButtonState aState, SkBitmap* anImage) {
+void ImageButton::SetImage(ButtonState aState, const SkBitmap* anImage) {
   images_[aState] = anImage ? *anImage : SkBitmap();
 }
 
 void ImageButton::SetBackground(SkColor color,
-                                SkBitmap* image,
-                                SkBitmap* mask) {
+                                const SkBitmap* image,
+                                const SkBitmap* mask) {
   if (!image || !mask) {
     background_image_.reset();
     return;
@@ -127,7 +127,8 @@
   SchedulePaint();
 }
 
-void ToggleImageButton::SetToggledImage(ButtonState state, SkBitmap* image) {
+void ToggleImageButton::SetToggledImage(ButtonState state,
+                                        const SkBitmap* image) {
   if (toggled_) {
     images_[state] = image ? *image : SkBitmap();
     if (state_ == state)
@@ -144,7 +145,7 @@
 ////////////////////////////////////////////////////////////////////////////////
 // ToggleImageButton, ImageButton overrides:
 
-void ToggleImageButton::SetImage(ButtonState state, SkBitmap* image) {
+void ToggleImageButton::SetImage(ButtonState state, const SkBitmap* image) {
   if (toggled_) {
     alternate_images_[state] = image ? *image : SkBitmap();
   } else {