Implement support for a Context parameter in image filters

Some upcoming work (support for expanding crop rects) requires
the clip bounds to be available during filter traversal. This change
replaces the SkMatrix parameter in the onFilterImage() traversals
with a Context parameter. It contains the CTM, as well as the clip
bounds.

BUG=skia:
R=reed@google.com

Review URL: https://codereview.chromium.org/189913021

git-svn-id: http://skia.googlecode.com/svn/trunk@13803 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/include/gpu/SkGpuDevice.h b/include/gpu/SkGpuDevice.h
index 94ca8d4..f8ee781 100644
--- a/include/gpu/SkGpuDevice.h
+++ b/include/gpu/SkGpuDevice.h
@@ -140,7 +140,8 @@
     virtual void makeRenderTargetCurrent();
 
     virtual bool canHandleImageFilter(const SkImageFilter*) SK_OVERRIDE;
-    virtual bool filterImage(const SkImageFilter*, const SkBitmap&, const SkMatrix&,
+    virtual bool filterImage(const SkImageFilter*, const SkBitmap&,
+                             const SkImageFilter::Context&,
                              SkBitmap*, SkIPoint*) SK_OVERRIDE;
 
     class SkAutoCachedTexture; // used internally