ahat: add support for diffing two heap dumps.

ahat now has the option to specify a --baseline hprof file to use as
the basis for comparing two heap dumps. When a baseline hprof file is
provided, ahat will highlight how the heap dump has changed relative
to the hprof file.

Differences that are highlighted include:
* overall heap sizes
* total bytes and number of allocations by type
* new and deleted instances of a given type
* retained sizes of objects
* instance fields, static fields, and array elements of modified objects

Also:
* Remove support for showing NativeAllocations, because I haven't ever
  found it to be useful, it is not obvious what a "native" allocation
  is, and I don't feel like adding diff support for them.
* Remove help page. Because it is outdated, not well maintained, and
  not very helpful in the first place.

Test: m ahat-test
Test: Run in diff mode for tests and added new tests for diff.
Test: Manually run with and without diff mode on heap dumps from system server.
Bug: 33770653
Change-Id: Id9a392ac75588200e716bbc3edbae6e9cd97c26b

1 files changed, 8 insertions, 1 deletions

diff --git a/tools/ahat/src/ObjectsHandler.java b/tools/ahat/src/ObjectsHandler.java
index 412647462c..3062d23b53 100644
--- a/tools/ahat/src/ObjectsHandler.java
+++ b/tools/ahat/src/ObjectsHandler.java
@@ -19,6 +19,7 @@ package com.android.ahat;
 import com.android.ahat.heapdump.AhatInstance;
 import com.android.ahat.heapdump.AhatSnapshot;
 import com.android.ahat.heapdump.Site;
+import com.android.ahat.heapdump.Sort;
 import java.io.IOException;
 import java.util.ArrayList;
 import java.util.Collections;
@@ -52,14 +53,20 @@ class ObjectsHandler implements AhatHandler {
     Collections.sort(insts, Sort.defaultInstanceCompare(mSnapshot));
 
     doc.title("Objects");
+
     doc.table(
         new Column("Size", Column.Align.RIGHT),
+        new Column("Δ", Column.Align.RIGHT, mSnapshot.isDiffed()),
         new Column("Heap"),
         new Column("Object"));
+
     SubsetSelector<AhatInstance> selector = new SubsetSelector(query, OBJECTS_ID, insts);
     for (AhatInstance inst : selector.selected()) {
+      AhatInstance base = inst.getBaseline();
       doc.row(
-          DocString.format("%,d", inst.getSize()),
+          DocString.format("%,14d", inst.getSize()),
+          DocString.delta(inst.isPlaceHolder(), base.isPlaceHolder(),
+            inst.getSize(), base.getSize()),
           DocString.text(inst.getHeap().getName()),
           Summarizer.summarize(inst));
     }