Removes clinits from very common core classes Boolean&Throwable.

[Boolean]
Earlier TRUE/FALSE fields were created with constructor. The constructor
requires to call clinit so TRUE/FALSE field initializations wasn't
inlined. As a result it caused TRUE/FALSE fields to be not hoistable via
constant hoisting pass; and as the fields were not hoisted; the clinit
was still required. Basically it was a chicken-egg problem. This CL uses
true/false primitives directly to initialize the fields so they are
hoisted and clinit is gone.
The Boolean.valueOf is also updated to not use the TRUE/FALSE fields to
avoid recursion in GWT (when primitive is assigned to boxed type in
TRUE/FALSE fields it would normally call Boolean.valueOf. Note that J2CL
takes the shortcut and not generates Boolean.valueOf calls).

[Throwable]
UNINITIALIZED marker object is upgraded to a compile time constant so
clinit is no longer needed.

Change-Id: Ic117889a5505f59b0e8c073e1d6523227fd921dd

user/super/com/google/gwt/emul/java/lang/Boolean.java

@@ -27,15 +27,9 @@
  * Wraps native <code>boolean</code> as an object.
  */
 public final class Boolean implements Comparable<Boolean>, Serializable {
-  /*
-   * TODO: figure out how to not clinit this class on direct field access.
-   */
 
-  // CHECKSTYLE_OFF: These have to be created somewhere.
-  public static final Boolean FALSE = new Boolean(false);
-  public static final Boolean TRUE = new Boolean(true);
-
-  // CHECKSTYLE_ON
+  public static final Boolean FALSE = false;
+  public static final Boolean TRUE = true;
 
   public static final Class<Boolean> TYPE = boolean.class;
 
@@ -69,7 +63,7 @@ public static String toString(boolean x) {
   }
 
   public static Boolean valueOf(boolean b) {
-    return b ? TRUE : FALSE;
+    return b ? $createBoolean(true) : $createBoolean(false);
   }
 
   public static Boolean valueOf(String s) {

user/super/com/google/gwt/emul/java/lang/Throwable.java

@@ -33,7 +33,7 @@
  */
 public class Throwable implements Serializable {
 
-  private static final Object UNITIALIZED = new Object();
+  private static final Object UNINITIALIZED = "__noinit__";
 
   /*
    * NOTE: We cannot use custom field serializers because we need the client and
@@ -55,7 +55,7 @@ public class Throwable implements Serializable {
   private transient boolean writetableStackTrace = true;
 
   @JsProperty
-  private transient Object backingJsObject = UNITIALIZED;
+  private transient Object backingJsObject = UNINITIALIZED;
 
   public Throwable() {
     fillInStackTrace();
@@ -176,7 +176,7 @@ public Throwable fillInStackTrace() {
       // If this is the first run, let constructor initialize it.
       // (We need to initialize the backingJsObject from constructor as our own implementation of
       // fillInStackTrace is not guaranteed to be executed.)
-      if (backingJsObject != UNITIALIZED) {
+      if (backingJsObject != UNINITIALIZED) {
         initializeBackingError();
       }