Rearrange emit vs emitIAS. Wait till function is done before dumping text.

Eventually, I wanted to have a flag "UseELFWriter" like:
https://codereview.chromium.org/678533005/diff/120001/src/IceCfg.cpp

Where the emit OStream would not have text, and only have
binary. This refactor hopefully means fewer places to
check for a flag to disable the text version of IAS,
and be able to write binary. Otherwise, there are some
text labels for branches that are still being dumped out.

BUG=none
R=stichnot@chromium.org

Review URL: https://codereview.chromium.org/700263003

src/assembler_ia32.h

diff --git a/src/assembler_ia32.h b/src/assembler_ia32.h
index 77159c4..a7ffc9e 100644
--- a/src/assembler_ia32.h
+++ b/src/assembler_ia32.h
@@ -364,7 +364,7 @@
   AssemblerX86 &operator=(const AssemblerX86 &) = delete;
 
 public:
-  explicit AssemblerX86(bool use_far_branches = false) : buffer_(*this) {
+  explicit AssemblerX86(bool use_far_branches = false) : Assembler() {
     // This mode is only needed and implemented for MIPS and ARM.
     assert(!use_far_branches);
     (void)use_far_branches;
@@ -829,15 +829,6 @@
     buffer_.FinalizeInstructions(region);
   }
 
-  // Expose the buffer, for bringup...
-  intptr_t GetPosition() const { return buffer_.GetPosition(); }
-  template <typename T> T LoadBuffer(intptr_t position) const {
-    return buffer_.Load<T>(position);
-  }
-  AssemblerFixup *GetLatestFixup(intptr_t position) const {
-    return buffer_.GetLatestFixup(position);
-  }
-
 private:
   inline void EmitUint8(uint8_t value);
   inline void EmitInt16(int16_t value);
@@ -868,8 +859,6 @@
   LabelVector LocalLabels;
 
   Label *GetOrCreateLabel(SizeT Number, LabelVector &Labels);
-
-  AssemblerBuffer buffer_;
 };
 
 inline void AssemblerX86::EmitUint8(uint8_t value) {