Refactor HGraphBuilder and SsaBuilder to remove HLocals

This patch merges the instruction-building phases from HGraphBuilder
and SsaBuilder into a single HInstructionBuilder class. As a result,
it is not necessary to generate HLocal, HLoadLocal and HStoreLocal
instructions any more, as the builder produces SSA form directly.

Saves 5-15% of arena-allocated memory (see bug for more data):
  GMS      20.46MB  =>  19.26MB  (-5.86%)
  Maps     24.12MB  =>  21.47MB  (-10.98%)
  YouTube  28.60MB  =>  26.01MB  (-9.05%)

Bug: 27894376
Change-Id: Iefe28d40600c169c5d306fd2c77034ae19476d90
diff --git a/compiler/optimizing/live_ranges_test.cc b/compiler/optimizing/live_ranges_test.cc
index 3202493..bdaef1d 100644
--- a/compiler/optimizing/live_ranges_test.cc
+++ b/compiler/optimizing/live_ranges_test.cc
@@ -211,8 +211,8 @@
    *
    * Which becomes the following graph (numbered by lifetime position):
    *       2: constant0
-   *       4: constant4
-   *       6: constant5
+   *       4: constant5
+   *       6: constant4
    *       8: goto
    *           |
    *       12: goto
@@ -247,7 +247,7 @@
   liveness.Analyze();
 
   // Test for the 0 constant.
-  LiveInterval* interval = liveness.GetInstructionFromSsaIndex(0)->GetLiveInterval();
+  LiveInterval* interval = graph->GetIntConstant(0)->GetLiveInterval();
   LiveRange* range = interval->GetFirstRange();
   ASSERT_EQ(2u, range->GetStart());
   // Last use is the loop phi so instruction is live until
@@ -256,18 +256,18 @@
   ASSERT_TRUE(range->GetNext() == nullptr);
 
   // Test for the 4 constant.
-  interval = liveness.GetInstructionFromSsaIndex(1)->GetLiveInterval();
+  interval = graph->GetIntConstant(4)->GetLiveInterval();
   range = interval->GetFirstRange();
   // The instruction is live until the end of the loop.
-  ASSERT_EQ(4u, range->GetStart());
+  ASSERT_EQ(6u, range->GetStart());
   ASSERT_EQ(24u, range->GetEnd());
   ASSERT_TRUE(range->GetNext() == nullptr);
 
   // Test for the 5 constant.
-  interval = liveness.GetInstructionFromSsaIndex(2)->GetLiveInterval();
+  interval = graph->GetIntConstant(5)->GetLiveInterval();
   range = interval->GetFirstRange();
   // The instruction is live until the return instruction after the loop.
-  ASSERT_EQ(6u, range->GetStart());
+  ASSERT_EQ(4u, range->GetStart());
   ASSERT_EQ(26u, range->GetEnd());
   ASSERT_TRUE(range->GetNext() == nullptr);