SkMultiPictureDraw API

This CL adds a new API to optimize across multiple SkPicture draw calls.

Note that multiple pictures rendered at once (i.e., picture piles) should be flattened into a single new picture that includes the required clipping on the different layers.

R=bsalomon@google.com, reed@google.com

Author: robertphillips@google.com

Review URL: https://codereview.chromium.org/491313003
diff --git a/gyp/core.gypi b/gyp/core.gypi
index 2cd317a..82f7057 100644
--- a/gyp/core.gypi
+++ b/gyp/core.gypi
@@ -116,6 +116,7 @@
         '<(skia_src_path)/core/SkMessageBus.h',
         '<(skia_src_path)/core/SkMetaData.cpp',
         '<(skia_src_path)/core/SkMipMap.cpp',
+        '<(skia_src_path)/core/SkMultiPictureDraw.cpp',
         '<(skia_src_path)/core/SkPackBits.cpp',
         '<(skia_src_path)/core/SkPaint.cpp',
         '<(skia_src_path)/core/SkPaintPriv.cpp',
@@ -275,6 +276,7 @@
         '<(skia_include_path)/core/SkMath.h',
         '<(skia_include_path)/core/SkMatrix.h',
         '<(skia_include_path)/core/SkMetaData.h',
+        '<(skia_include_path)/core/SkMultiPictureDraw.h',
         '<(skia_include_path)/core/SkOnce.h',
         '<(skia_include_path)/core/SkOSFile.h',
         '<(skia_include_path)/core/SkPackBits.h',