Sketch splitting SkPicture into an interface and SkBigPicture.

Adds small pictures for drawRect(), drawTextBlob(), and drawPath().
These cover about 89% of draw calls from Blink SKPs,
and about 25% of draw calls from our GMs.

SkPicture handles:
  - serialization and deserialization
  - unique IDs

Everything else is left to the subclasses:
  - playback(), cullRect()
  - hasBitmap(), hasText(), suitableForGPU(), etc.
  - LayerInfo / AccelData if applicable.

The time to record a 1-op picture improves a good chunk
(2 mallocs to 1), and the time to record a 0-op picture
greatly improves (2 mallocs to none):

    picture_overhead_draw:   450ns -> 350ns
    picture_overhead_nodraw: 300ns -> 90ns

BUG=skia:

Committed: https://skia.googlesource.com/skia/+/c92c129ff85b05a714bd1bf921c02d5e14651f8b

Latest blink_linux_rel:

http://build.chromium.org/p/tryserver.blink/builders/linux_blink_rel/builds/61248

Committed: https://skia.googlesource.com/skia/+/15877b6eae33a9282458bdb904a6d00440eca0ec

http://build.chromium.org/p/tryserver.blink/builders/linux_blink_rel/builds/62015

Review URL: https://codereview.chromium.org/1112523006
diff --git a/src/core/SkRecordDraw.cpp b/src/core/SkRecordDraw.cpp
index ba15c1b..65e6d49 100644
--- a/src/core/SkRecordDraw.cpp
+++ b/src/core/SkRecordDraw.cpp
@@ -587,7 +587,7 @@
 class CollectLayers : SkNoncopyable {
 public:
     CollectLayers(const SkRect& cullRect, const SkRecord& record,
-                  const SkPicture::SnapshotArray* pictList, SkLayerInfo* accelData)
+                  const SkBigPicture::SnapshotArray* pictList, SkLayerInfo* accelData)
         : fSaveLayersInStack(0)
         , fAccelData(accelData)
         , fPictList(pictList)
@@ -640,10 +640,10 @@
     void trackSaveLayersForPicture(const SkPicture* picture, const SkPaint* paint) {
         // For sub-pictures, we wrap their layer information within the parent
         // picture's rendering hierarchy
-        SkPicture::AccelData::Key key = SkLayerInfo::ComputeKey();
-
-        const SkLayerInfo* childData =
-            static_cast<const SkLayerInfo*>(picture->EXPERIMENTAL_getAccelData(key));
+        const SkLayerInfo* childData = NULL;
+        if (const SkBigPicture* bp = picture->asSkBigPicture()) {
+            childData = static_cast<const SkLayerInfo*>(bp->accelData());
+        }
         if (!childData) {
             // If the child layer hasn't been generated with saveLayer data we
             // assume the worst (i.e., that it does contain layers which nest
@@ -774,7 +774,7 @@
     // The op code indices of all the currently active saveLayers
     SkTDArray<unsigned>      fSaveLayerOpStack;
     SkLayerInfo*             fAccelData;
-    const SkPicture::SnapshotArray* fPictList;
+    const SkBigPicture::SnapshotArray* fPictList;
 
     SkRecords::FillBounds fFillBounds;
 };
@@ -793,7 +793,7 @@
 }
 
 void SkRecordComputeLayers(const SkRect& cullRect, const SkRecord& record,
-                           const SkPicture::SnapshotArray* pictList, SkBBoxHierarchy* bbh,
+                           const SkBigPicture::SnapshotArray* pictList, SkBBoxHierarchy* bbh,
                            SkLayerInfo* data) {
     SkRecords::CollectLayers visitor(cullRect, record, pictList, data);