Add SkBBoxHierarchy::reserve() as an optional size hint.

I want to play around with how SkTileGrid stores its tiles.  Having a
cap on the number of insert() calls can be pretty handy.

While I'm at it, I gave flush() a default empty impl.  Like reserve(),
it's really an optional hook for subclasses.

BUG=skia:

Review URL: https://codereview.chromium.org/639933003

src/core/SkBBoxHierarchy.h

@@ -24,9 +24,14 @@ public:
     SkBBoxHierarchy() {}
 
     /**
-     * Insert opIndex and corresponding bounding box
+     * Hint that <= opCount calls to insert() will be made.
+     */
+    virtual void reserve(unsigned opCount) {}
+
+    /**
+     * Insert opIndex and corresponding bounding box.
      * @param opIndex Any value, will be returned in order.
-     * @param bounds The bounding box, should not be empty
+     * @param bounds The bounding box, should not be empty.
      * @param defer Whether or not it is acceptable to delay insertion of this element (building up
      *        an entire spatial data structure at once is often faster and produces better
      *        structures than repeated inserts) until flushDeferredInserts is called or the first
@@ -35,9 +40,9 @@ public:
     virtual void insert(unsigned opIndex, const SkRect& bounds, bool defer = false) = 0;
 
     /**
-     * If any insertions have been deferred, this forces them to be inserted
+     * If any insertions have been deferred, force them to be inserted.
      */
-    virtual void flushDeferredInserts() = 0;
+    virtual void flushDeferredInserts() {}
 
     /**
      * Populate results with sorted opIndex corresponding to bounding boxes that intersect query.

src/core/SkRecordDraw.cpp

@@ -162,6 +162,7 @@ public:
 
         // Finally feed all stored bounds into the BBH.  They'll be returned in this order.
         SkASSERT(bbh);
+        bbh->reserve(record.count());
         for (unsigned i = 0; i < record.count(); i++) {
             if (!fBounds[i].isEmpty()) {
                 bbh->insert(i, fBounds[i], true/*ok to defer*/);

src/core/SkTileGrid.h

@@ -30,8 +30,6 @@ public:
      */
     virtual void insert(unsigned opIndex, const SkRect& bounds, bool) SK_OVERRIDE;
 
-    virtual void flushDeferredInserts() SK_OVERRIDE {};
-
     /**
      * Populate 'results' with opIndexes corresponding to bounding boxes that intersect 'query'.
      * This will be fastest if the query is an exact match to a single grid tile.

tests/PictureTest.cpp

@@ -1869,9 +1869,7 @@ struct CountingBBH : public SkBBoxHierarchy {
         this->searchCalls++;
     }
 
-    // All other methods unimplemented.
     virtual void insert(unsigned opIndex, const SkRect& bounds, bool defer) SK_OVERRIDE {}
-    virtual void flushDeferredInserts() SK_OVERRIDE {}
 };
 
 class SpoonFedBBHFactory : public SkBBHFactory {

tests/RecordDrawTest.cpp

@@ -103,7 +103,6 @@ struct TestBBH : public SkBBoxHierarchy {
         fEntries.push(e);
     }
 
-    virtual void flushDeferredInserts() SK_OVERRIDE {}
     virtual void search(const SkRect& query, SkTDArray<unsigned>* results) const SK_OVERRIDE {}
 
     struct Entry {